Fix -Wnarrowing warnings in KDSingleApplicationGuard

src/libcalamares/kdsingleapplicationguard/kdtoolsglobal.cpp

@@ -21,12 +21,16 @@ namespace {
 static Version kdParseQtVersion( const char * const version ) {
     if ( !version || qstrlen( version ) < 5 || version[1] != '.' || version[3] != '.' || ( version[5] != 0 && version[5] != '.' && version[5] != '-' ) )
 	return Version(); // parse error
-    const Version result = { { version[0] - '0', version[2] - '0', version[4] - '0' } };
+    const Version result = { { static_cast< unsigned char >( version[0] - '0' ),
+                               static_cast< unsigned char >( version[2] - '0' ),
+                               static_cast< unsigned char >( version[4] - '0' ) } };
     return result;
 }
 
 bool _kdCheckQtVersion_impl( int major, int minor, int patchlevel ) {
     static const Version actual = kdParseQtVersion( qVersion() ); // do this only once each run...
-    const Version requested = { { major, minor, patchlevel } };
+    const Version requested = { { static_cast< unsigned char >( major ),
+                                  static_cast< unsigned char >( minor ),
+                                  static_cast< unsigned char >( patchlevel ) } };
     return actual >= requested;
 }