Merge ElementsProject#702: fix no return at end of function introduce…

…d in 172ad71

72186f8 f'Fix QT startup for custom chains' (Gregory Sanders)

Pull request description:

Tree-SHA512: b903ae09eeaf5a660444a69c8f058712a808f04ae5c037474c98d013077c80f39b697d679ec07d877188c2e53a93c8f7bcbf2bca1803ee6a43dd0b8eada1f962

src/qt/networkstyle.cpp

@@ -93,4 +93,5 @@ const NetworkStyle* NetworkStyle::instantiate(const std::string& networkId)
                     titleAddText.c_str());
         }
     }
+    return nullptr;
 }