fix for GrAtlasTextContext occasionally crashes on mixed runs

src/gpu/GrAtlasTextContext.cpp

Index: src/gpu/GrAtlasTextContext.cpp
diff --git a/src/gpu/GrAtlasTextContext.cpp b/src/gpu/GrAtlasTextContext.cpp
index 91527aba64885ac3b31605a0d746a4fb021c76a8..c1d3e0f33dfb82f7f5b0b23334d9975d3d4a989f 100644
--- a/src/gpu/GrAtlasTextContext.cpp
+++ b/src/gpu/GrAtlasTextContext.cpp
@@ -1282,7 +1282,7 @@ void GrAtlasTextContext::bmpAppendGlyph(GrAtlasTextBlob* blob, int runIndex,
 
     PerSubRunInfo* subRun = &run.fSubRunInfo.back();
     if (run.fInitialized && subRun->fMaskFormat != format) {
-        subRun = &run.fSubRunInfo.push_back();
+        subRun = &run.push_back();
     }
 
     run.fInitialized = true;