Notify glyph parsing errors

Emit a signal when the glyphs are not parsed correctly.

src/mbgl/text/glyph_pbf.cpp

@@ -23,14 +23,14 @@ GlyphPBF::GlyphPBF(const std::string& glyphURL,
                    const GlyphLoadingFailedCallback& failureCallback)
     : parsed(false), env(env_) {
     // Load the glyph set URL
-    std::string url = util::replaceTokens(glyphURL, [&](const std::string &name) -> std::string {
+    url = util::replaceTokens(glyphURL, [&](const std::string &name) -> std::string {
         if (name == "fontstack") return util::percentEncode(fontStack);
         if (name == "range") return util::toString(glyphRange.first) + "-" + util::toString(glyphRange.second);
         return "";
     });
 
     // The prepare call jumps back to the main thread.
-    req = env.request({ Resource::Kind::Glyphs, url }, [&, url, successCallback, failureCallback](const Response &res) {
+    req = env.request({ Resource::Kind::Glyphs, url }, [&, successCallback, failureCallback](const Response &res) {
         req = nullptr;
 
         if (res.status != Response::Successful) {

src/mbgl/text/glyph_pbf.hpp

@@ -29,6 +29,10 @@ public:
     void parse(FontStack &stack);
     bool isParsed() const;
 
+    std::string getURL() const {
+        return url;
+    }
+
 private:
     GlyphPBF(const GlyphPBF &) = delete;
     GlyphPBF(GlyphPBF &&) = delete;
@@ -36,6 +40,7 @@ private:
     GlyphPBF &operator=(GlyphPBF &&) = delete;
 
     std::string data;
+    std::string url;
     std::atomic<bool> parsed;
 
     Environment& env;

src/mbgl/text/glyph_store.cpp

@@ -34,8 +34,14 @@ bool GlyphStore::requestGlyphRangesIfNeeded(const std::string& fontStackName,
 
     auto successCallback = [this, fontStackName](GlyphPBF* glyph) {
         auto fontStack = createFontStack(fontStackName);
-        glyph->parse(**fontStack);
-        asyncEmitGlyphRangeLoaded->send();
+        try {
+            glyph->parse(**fontStack);
+            asyncEmitGlyphRangeLoaded->send();
+        } catch (const std::exception&) {
+            std::lock_guard<std::mutex> lock(errorMessageMutex);
+            errorMessage = "Failed to parse [" + glyph->getURL() + "]";
+            asyncEmitGlyphRangeLoadedingFailed->send();
+        }
     };
 
     auto failureCallback = [this](const std::string& message) {