ArrayMesh::add_surface_from_arrays crashes

Hello, when trying to call `ArrayMesh::add_surface_from_arrays` from gdnative, I get a crash. Doing the exact same call from GDscript (with the array computed by gdnative) works well.

## My setup
- archlinux
- gcc `11.1.0`
- godot version `3.4.2.stable.arch_linux` (also tested with binary from `godotengine.org 3.4.2.stable.official.45eaa2daf`)
- godot-cpp version `godot-3.4.1-stable` (also tested 3.3.4 and 3.1.1)

## Minimal reproduction

I suggest to use `gdnative_cpp_example` because it is a good minimal reference, but really any gdnative plugin should do. It is just about writing 9 lines of codes, that make godot crashes at runtime.

- Get the example repo https://github.com/BastiaanOlij/gdnative_cpp_example with submodules
- Compile godot-cpp (`scons platform=linux generate_bindings=yes` in `gdnative_cpp_example/godot-cpp`)
- Add the following to `GDExample::_process` implementation in `src/gdexample.cpp` (you need to `#include ` as well):
```cpp
Array arr;
arr.resize(ArrayMesh::ARRAY_MAX);
ArrayMesh arrayMesh;
PoolVector3Array verts;
verts.append(Vector3(0, 0, 0));
verts.append(Vector3(0, 0, 1));
verts.append(Vector3(0, 0, 2));
arr[ArrayMesh::ARRAY_VERTEX] = verts;
arrayMesh.add_surface_from_arrays(Mesh::PRIMITIVE_TRIANGLES, arr);
```
- Compile the gdnative lib with `scons platform=linux` in `gdnative_cpp_example` folder
- Launch the demo project

## The crash

Godot crashes with the following:
```
handle_crash: Program crashed with signal 11
Engine version: Godot Engine v3.4.2.stable.arch_linux
Dumping the backtrace. Please include this when reporting the bug on https://github.com/godotengine/godot/issues
[1] /usr/lib/libc.so.6(+0x3cda0) [0x7f2df9197da0] (??:0)
[2] godot(+0x2283be3) [0x55e184168be3] (??:0)
[3] godot(+0x2294e14) [0x55e184179e14] (??:0)
[4] godot::ArrayMesh::add_surface_from_arrays(long, godot::Array, godot::Array, long) (??:0)
[5] godot::GDExample::_process(float) (??:0)
[6] godot_variant godot::__wrapped_method(void*, void*, void*, int, godot_variant**) (??:0)
[7] godot(+0xcf59e8) [0x55e182bda9e8] (??:0)
[8] godot(+0x1b8f13f) [0x55e183a7413f] (??:0)
[9] godot(+0x20acae8) [0x55e183f91ae8] (??:0)
[10] godot(+0x1ba93ee) [0x55e183a8e3ee] (??:0)
[11] godot(+0x1bc3eb1) [0x55e183aa8eb1] (??:0)
[12] godot(+0x8b9a25) [0x55e18279ea25] (??:0)
[13] godot(+0x8359a5) [0x55e18271a9a5] (??:0)
[14] /usr/lib/libc.so.6(__libc_start_main+0xd5) [0x7f2df9182b25] (??:0)
[15] godot(+0x84991e) [0x55e18272e91e] (??:0)
-- END OF BACKTRACE --
```

gdb gives a little more info. It says it comes from a `SIGSEGV`, but in my other project (too cumbersome to share here) it is a `SIGBUS`. Callstack for the minimal reproduction is:
```
(gdb) bt
#0 0x00005555577d7be3 in ?? ()
#1 0x00005555577e8e14 in ?? ()
#2 0x00007fffd887e2ec in godot::___godot_icall_void_int_Array_Array_int (arg3=, arg2=..., arg1=...,
arg0=, inst=0x7fffffffced0, mb=) at include/gen/__icalls.hpp:3348
#3 godot::ArrayMesh::add_surface_from_arrays (this=this@entry=0x7fffffffcf60, primitive=primitive@entry=4, arrays=...,
blend_shapes=..., compress_flags=compress_flags@entry=97280) at src/gen/ArrayMesh.cpp:57
#4 0x00007fffd879072a in godot::GDExample::_process (this=0x55555f7ec680, delta=0.149999976) at src/gdexample.cpp:38
#5 0x00007fffd8790ac4 in godot::_WrappedMethod::apply<0> (args=0x7fffffffd0b8, obj=,
this=0x7fffffffcfd0) at godot-cpp/include/core/Godot.hpp:263
#6 godot::__wrapped_method (method_data=0x7fffffffcfd0, user_data=, args=0x7fffffffd0b8)
at godot-cpp/include/core/Godot.hpp:278
#7 0x00005555562499e8 in ?? ()
#8 0x00005555570e313f in ?? ()
#9 0x0000555557600ae8 in ?? ()
#10 0x00005555570fd3ee in ?? ()
#11 0x0000555557117eb1 in ?? ()
#12 0x0000555555e0da25 in ?? ()
#13 0x0000555555d899a5 in ?? ()
#14 0x00007ffff51a2b25 in __libc_start_main () from /usr/lib/libc.so.6
#15 0x0000555555d9d91e in ?? ()
```

## Note

I don't know what is happening here or how to circonvent the issue. I have made some interesting finds though:
- The same code written in GDscript works well, so it’s not an issue of the arguments beeing incorrect.
- The call from `add_surface_from_arrays` does not always crash:
* If the input array is empty, it instead properly complains that this should be of size 9
* If the input array is of size 9 but without vertices, it instead properly complains it needs vertices
* And the strangest of all, I forgot to add the vertices to the array at some point, leading to this very weird discovery (read the comment):
```cpp
Array arr;
arr.resize(ArrayMesh::ARRAY_MAX);
ArrayMesh arrayMesh;
PoolVector3Array verts;
verts.append(Vector3(0, 0, 0)); // <-- Without this line there is no crash, but with it there is!
// Even though the line should have no effect because "verts" is never used
arrayMesh.add_surface_from_arrays(Mesh::PRIMITIVE_TRIANGLES, arr);
```