ImFontAtlas: Fixed multiple rebuild with same inputs erroneously increased ConfigDataCount. CI: Update Ubuntu 18.04 > 20.04 (motivated by #3369)

Fix Freetype warning.

.github/workflows/build.yml

@@ -180,7 +180,7 @@ jobs:
         run: '"%MSBUILD_PATH%\MSBuild.exe" examples/example_win32_directx12/example_win32_directx12.vcxproj /p:Platform=x64 /p:Configuration=Release'
 
   Linux:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
     - uses: actions/checkout@v1
       with:

imgui_draw.cpp

@@ -2328,6 +2328,7 @@ void ImFontAtlasBuildSetupFont(ImFontAtlas* atlas, ImFont* font, ImFontConfig* f
         font->ClearOutputData();
         font->FontSize = font_config->SizePixels;
         font->ConfigData = font_config;
+        font->ConfigDataCount = 0;
         font->ContainerAtlas = atlas;
         font->Ascent = ascent;
         font->Descent = descent;

misc/freetype/imgui_freetype.cpp

@@ -382,7 +382,7 @@ bool ImFontAtlasBuildWithFreeType(FT_Library ft_library, ImFontAtlas* atlas, uns
             dst_tmp.GlyphsSet.Create(dst_tmp.GlyphsHighest + 1);
 
         for (const ImWchar* src_range = src_tmp.SrcRanges; src_range[0] && src_range[1]; src_range += 2)
-            for (int codepoint = src_range[0]; codepoint <= src_range[1]; codepoint++)
+            for (int codepoint = src_range[0]; codepoint <= (int)src_range[1]; codepoint++)
             {
                 if (dst_tmp.GlyphsSet.TestBit(codepoint))    // Don't overwrite existing glyphs. We could make this an option (e.g. MergeOverwrite)
                     continue;