Fix usage uic-tqt without an '.ui' file in arguments

This resolves issues with mode 'embed'

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit be944e140b)

qtinterface/uic-tqt.cmake

@@ -10,9 +10,13 @@ else
 		fi
 	done
 
-	cp -Rp $uifile $uifile.bkp
-	tqt-replace $uifile
+	if [[ "$uifile" != "" ]]; then
+		cp -Rp $uifile $uifile.bkp
+		tqt-replace $uifile
+	fi
 	@UIC_EXECUTABLE@ "$@"
-	cp -Rp $uifile.bkp $uifile
-	rm -f $uifile.bkp
+	if [[ "$uifile" != "" ]]; then
+		cp -Rp $uifile.bkp $uifile
+		rm -f $uifile.bkp
+	fi
 fi