shell32: Fix a mem leak on an error path. Found by Smatch.

dlls/shell32/shfldr_mycomp.c

@@ -684,6 +684,7 @@ static HRESULT WINAPI ISF_MyComputer_fnGetDisplayNameOf (IShellFolder2 *iface,
         {
             /* Neither a shell namespace extension nor a drive letter. */
             ERR("Wrong pidl type\n");
+            CoTaskMemFree(pszPath);
             return E_INVALIDARG;
         }
     }