If bitmap buffer is empty, do not render anything

[radarhere]

Resolves #8272

#6846 added an error if the bitmap buffer is empty. https://github.com/python-pillow/Pillow/blob/d6cfebd016db25549d05a9c5caa2ef3b53cff5c5/src/_imagingft.c#L1028-L1032

However, this new issue found the buffer is empty for a space character in a particular font, which seems like a realistic scenario, and has been confirmed as valid by one of the FreeType maintainers - https://github.com/python-pillow/Pillow/issues/8272#issuecomment-2305870693

So if the bitmap buffer is empty, this PR just doesn't draw anything, uses the advances to update the position for the next character, and moves on.

[nulano]

We might want to add a test that triggers the if (stroker != NULL) branch in font_render to make sure that passing such a glyph to the stroker API is safe.

[radarhere]

You're concerned about passing a glyph where bitmap buffer is empty to this block? test_bitmap_font_stroke actually already does this.

[apodtele]

Note then the glyph outline in question is not empty but degenerate. It contains two points but still produces a blank space. In this particular case, it results in a 0×1 bitmap, aka one empty row. Do not check for bitmap.rows, or check both dimentions

[radarhere]

The glyph outline may not be empty, but the bitmap buffer is. From my understanding, we're safe to skip drawing and just advance if that is the case. I presume the size of the glyph does not affect the advance.

[apodtele]

Correct, just advance if the buffer is NULL regardless of its dimensions. You have sufficient error checking from FreeType calls.