PIString::arg() now ignore non-suitable %.

PIVector and PIDeque now use std::stable_sort

libs/main/text/pistring.cpp

@@ -536,7 +536,7 @@ PIString PIString::minArgPlaceholder() {
 			bool ok = false;
 			tmp     = mid(i + 1, j - i - 1);
 			int cur = tmp.toInt(10, &ok);
-			if (!ok) continue;
+			if (!ok || tmp.isEmpty()) continue;
 			if (min < 0 || min > cur) {
 				min = cur;
 				ret = tmp;