Fix memory leaks in title_format.

This fixes three memory leaks that were found during the implementation of #2120
so that they can be fixed in a bugfix release.

relates to #2143

src/util.c

@@ -332,6 +332,20 @@ void *memmem(const void *l, size_t l_len, const void *s, size_t s_len) {
 
 #endif
 
+/*
+ * Escapes the given string if a pango font is currently used.
+ * If the string has to be escaped, the input string will be free'd.
+ *
+ */
+char *pango_escape_markup(char *input) {
+    if (!font_is_pango())
+        return input;
+
+    char *escaped = g_markup_escape_text(input, -1);
+    FREE(input);
+    return escaped;
+}
+
 /*
  * Handler which will be called when we get a SIGCHLD for the nagbar, meaning
  * it exited (or could not be started, depending on the exit code).