Fix missing return statement in static bool method

Looks like devtoolset compiler behaves differently on bool methods
without an explicit return statement. Kind of strange.

Undefined behavior?

src/core/appdir_root_setup.cpp

@@ -77,6 +77,8 @@ namespace linuxdeploy {
                     ldLog() << LD_ERROR << "Could not find suitable icon for Icon entry:" << iconEntry.value() << std::endl;
                     return false;
                 }
+
+                return true;
             }
 
             bool deployCustomAppRunFile(const bf::path& customAppRunPath) const {