ImFontAtlas: Handle stb_truetype failure more gracefully, GetTexDataAsRGBA32() won't crash during conversion. (#1527)

imgui_draw.cpp

@@ -1439,12 +1439,15 @@ void    ImFontAtlas::GetTexDataAsRGBA32(unsigned char** out_pixels, int* out_wid
     {
         unsigned char* pixels;
         GetTexDataAsAlpha8(&pixels, NULL, NULL);
+        if (pixels)
+        {
             TexPixelsRGBA32 = (unsigned int*)ImGui::MemAlloc((size_t)(TexWidth * TexHeight * 4));
             const unsigned char* src = pixels;
             unsigned int* dst = TexPixelsRGBA32;
             for (int n = TexWidth * TexHeight; n > 0; n--)
                 *dst++ = IM_COL32(255, 255, 255, (unsigned int)(*src++));
         }
+    }
 
     *out_pixels = (unsigned char*)TexPixelsRGBA32;
     if (out_width) *out_width = TexWidth;
@@ -1683,6 +1686,7 @@ bool    ImFontAtlasBuildWithStbTruetype(ImFontAtlas* atlas)
         IM_ASSERT(font_offset >= 0);
         if (!stbtt_InitFont(&tmp.FontInfo, (unsigned char*)cfg.FontData, font_offset))
         {
+            atlas->TexWidth = atlas->TexHeight = 0; // Reset output on failure
             ImGui::MemFree(tmp_array);
             return false;
         }