re-add sprite atlas pollution fix

It got missed in a merge.
03d5e2da80

src/mbgl/text/quads.cpp

@@ -157,7 +157,8 @@ SymbolQuads getGlyphQuads(Anchor &anchor, const Shaping &shapedText,
         }
 
         // The rects have an addditional buffer that is not included in their size;
-        const float rectBuffer = 3.0f;
+        const float glyphPadding = 1.0f;
+        const float rectBuffer = 3.0f + glyphPadding;
 
         const float x1 = positionedGlyph.x + glyph.metrics.left - rectBuffer;
         const float y1 = positionedGlyph.y - glyph.metrics.top - rectBuffer;