Fix ImageClearBackground (#1711)

- Dividing by height instead of width results in missing parts of the image.

src/textures.c

@@ -2347,7 +2347,7 @@ Rectangle GetImageAlphaBorder(Image image, float threshold)
 // Clear image background with given color
 void ImageClearBackground(Image *dst, Color color)
 {
-    for (int i = 0; i < dst->width*dst->height; ++i) ImageDrawPixel(dst, i%dst->width, i/dst->height, color);
+    for (int i = 0; i < dst->width*dst->height; ++i) ImageDrawPixel(dst, i%dst->width, i/dst->width, color);
 }
 
 // Draw pixel within an image