Plotline with stride parameter caused index out of bound exception.

Issue code is here in _**implot_internal.h**_:

``` cpp
template
inline T OffsetAndStride(const T* data, int idx, int count, int offset, int stride) {
idx = ImPosMod(offset + idx, count);

return *(const T*)(const void*)((const unsigned char*)data + (size_t)idx * stride); // this line
}
```

I tried to debug the reason of this issue and found that some times the idx * stride is more bigger than count * sizeof(T).

Tried one fix but not worked, plotted line will at a mess when set to idx to max size when it is too big.
Should have deeper reason for this.

Hope some one will fix this some time, and I just stride data before we start plot to avoid this.

Thank you.