fix crash bug for styles that have no glyph url specified

include/mbgl/text/glyph_store.hpp

@@ -62,13 +62,15 @@ private:
 // Manages Glyphrange PBF loading.
 class GlyphStore {
 public:
-    GlyphStore(const std::string &glyphURL);
+    GlyphStore();
 
     // Block until all specified GlyphRanges of the specified font stack are loaded.
     void waitForGlyphRanges(const std::string &fontStack, const std::set<GlyphRange> &glyphRanges);
 
     FontStack &getFontStack(const std::string &fontStack);
 
+    void setURL(const std::string &url);
+
 private:
     // Loads an individual glyph range from the font stack and adds it to rangeSets
     std::shared_future<GlyphPBF &> loadGlyphRange(const std::string &fontStack, std::map<GlyphRange, std::unique_ptr<GlyphPBF>> &rangeSets, GlyphRange range);
@@ -76,7 +78,7 @@ private:
     FontStack &createFontStack(const std::string &fontStack);
 
 public:
-    const std::string glyphURL;
+    std::string glyphURL;
 
 private:
     std::unordered_map<std::string, std::map<GlyphRange, std::unique_ptr<GlyphPBF>>> ranges;

src/map/map.cpp

@@ -33,6 +33,7 @@ Map::Map(View& view)
       transform(view),
       style(std::make_shared<Style>()),
       glyphAtlas(std::make_shared<GlyphAtlas>(1024, 1024)),
+      glyphStore(std::make_shared<GlyphStore>()),
       spriteAtlas(std::make_shared<SpriteAtlas>(512, 512)),
       texturepool(std::make_shared<Texturepool>()),
       painter(*this),
@@ -187,6 +188,7 @@ void Map::setStyleJSON(std::string newStyleJSON) {
     styleJSON.swap(newStyleJSON);
     sprite.reset();
     style->loadJSON((const uint8_t *)styleJSON.c_str());
+    glyphStore->setURL(style->glyph_url);
     update();
 }
 
@@ -514,16 +516,6 @@ void Map::prepare() {
     bool dimensionsChanged = oldState.getFramebufferWidth() != state.getFramebufferWidth() ||
                              oldState.getFramebufferHeight() != state.getFramebufferHeight();
 
-    // Create a new glyph store object in case the glyph URL changed.
-    // TODO: Move this to a less frequently called place; we only need to do this when the
-    // stylesheet changes.
-    if (glyphStore && glyphStore->glyphURL != style->glyph_url) {
-        glyphStore.reset();
-    }
-    if (!glyphStore && style->glyph_url.size()) {
-        glyphStore = std::make_shared<GlyphStore>(style->glyph_url);
-    }
-
     if (pixelRatioChanged || dimensionsChanged) {
         painter.clearFramebuffers();
     }

src/text/glyph_store.cpp

@@ -226,12 +226,19 @@ void GlyphPBF::parse(FontStack &stack) {
     data.clear();
 }
 
-GlyphStore::GlyphStore(const std::string &glyphURL)
-    : glyphURL(glyphURL) {}
+GlyphStore::GlyphStore() {}
+
+void GlyphStore::setURL(const std::string &url) {
+    glyphURL = url;
+}
+
 
 void GlyphStore::waitForGlyphRanges(const std::string &fontStack, const std::set<GlyphRange> &glyphRanges) {
     // We are implementing a blocking wait with futures: Every GlyphSet has a future that we are
     // waiting for until it is loaded.
+    if (glyphRanges.empty()) {
+        return;
+    }
 
     FontStack *stack = nullptr;