don't leak vertex data if text is scaled to 0

stb_truetype.h

@@ -2435,7 +2435,10 @@ STBTT_DEF unsigned char *stbtt_GetGlyphBitmapSubpixel(const stbtt_fontinfo *info
 
    if (scale_x == 0) scale_x = scale_y;
    if (scale_y == 0) {
-      if (scale_x == 0) return NULL;
+      if (scale_x == 0) {
+         STBTT_free(vertices, info->userdata);
+         return NULL;
+      }
       scale_y = scale_x;
    }