Android: Avoid "Empty filename passed to function" warning

When launching Qt Creator with clean settings on Windows, the Android
plugin might cause an "Empty filename passed to function" warning that
comes from deep inside Qt.

This hack works around that.

Change-Id: Id668b981a1467a54d852082e95963e34554006e9
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/plugins/android/androidconfigurations.cpp

@@ -505,6 +505,9 @@ FilePath AndroidConfig::toolchainPathFromNdk(const FilePath &ndkLocation, OsType
         toolchainPath = tcPath / llvmIter.fileName() / "prebuilt/";
     }
 
+    if (toolchainPath.isEmpty())
+        return {};
+
     // detect toolchain host
     QStringList hostPatterns;
     switch (hostOs) {