[PDF] Fix font width generation when glyph 0 is used.

src/core/SkAdvancedTypefaceMetrics.cpp

Index: src/core/SkAdvancedTypefaceMetrics.cpp
diff --git a/src/core/SkAdvancedTypefaceMetrics.cpp b/src/core/SkAdvancedTypefaceMetrics.cpp
index ce64a42d0a9bfb2cbce7d7d405c3db4d217b2254..f9b25dc96aac1808cf59e6dbea403fa3d8e2024c 100644
--- a/src/core/SkAdvancedTypefaceMetrics.cpp
+++ b/src/core/SkAdvancedTypefaceMetrics.cpp
@@ -169,6 +169,8 @@ SkAdvancedTypefaceMetrics::AdvanceMetric<Data>* getAdvanceData(
         Data advance = kInvalidAdvance;
         if (gId < lastIndex) {
             // Get glyph id only when subset is NULL, or the id is in subset.
+            SkASSERT(!subsetGlyphIDs || (subsetIndex < subsetGlyphIDsLength &&
+                    static_cast<uint32_t>(gId) <= subsetGlyphIDs[subsetIndex]));
             if (!subsetGlyphIDs ||
                 (subsetIndex < subsetGlyphIDsLength &&
                  static_cast<uint32_t>(gId) == subsetGlyphIDs[subsetIndex])) {