Bug 1419004: Fix crash when setting plugin process names on macOS 10.13.2. r=mstange

dom/plugins/ipc/PluginUtilsOSX.mm

@@ -249,6 +249,11 @@ bool mozilla::plugins::PluginUtilsOSX::SetProcessName(const char* aProcessName)
   if (!sApplicationASN) {
     sApplicationASN = ::CFBundleGetFunctionPointerForName(launchServices, 
                                             CFSTR("_LSGetCurrentApplicationASN"));
+    if (!sApplicationASN) {
+      NS_WARNING("Failed to set process name: Could not get function pointer "
+                 "for LaunchServices");
+      return false;
+    }
   }
 
   LSGetASNType getASNFunc = reinterpret_cast<LSGetASNType>