PVS-Studio: Not all members of a class are initialized inside the constructor.

We have found bugs using PVS-Studio tool. PVS-Studio is a static code analyzer for C, C++ and C#: https://www.viva64.com/en/pvs-studio/

We suggests having a look at the emails, sent from @pvs-studio.com.

[V730](https://www.viva64.com/en/w/V730/) Not all members of a class are initialized inside the constructor. Consider inspecting: **data_mode**. image.cc 315

```
....
enum data_mode_t {
DATA_IMAGE = 1
, DATA_MIME = 2
} data_mode;
....

Image::Image() {
filename = NULL;
_data = NULL;
_data_len = 0;
_surface = NULL;
width = height = 0;
state = DEFAULT;
onload = NULL;
onerror = NULL;
}
```
There are many such fragments in the code, here are some of them:

- V730 Not all members of a class are initialized inside the constructor. Consider inspecting: _path. canvasrenderingcontext2d.cc 150
- V730 Not all members of a class are initialized inside the constructor. Consider inspecting: isolate_, prev_next_, prev_limit_. v8.h 908
- V730 Not all members of a class are initialized inside the constructor. Consider inspecting: str_st_. nan.h 907

Start with the PVS-Studio V730 report in image.cc at line 315, then inspect the related reports in canvasrenderingcontext2d.cc, v8.h, and nan.h. Review the affected constructors and determine the complete set of reported uninitialized members; done means the identified V730 findings are addressed and the relevant checks pass.

Written by the indexing model from the issue text.