Fix TQString::sprintf() not calling va_end() in case of bad cformat

Also rearrange code a bit so it would be obvious that the function
doesn't return a dangling reference.

Signed-off-by: Alexander Golubev <fatzer2@gmail.com>
(cherry picked from commit bcda401191)

src/tools/qstring.cpp

@@ -2622,13 +2622,12 @@ TQString &TQString::sprintf(const char *cformat, ...)
     if ( !cformat || !*cformat ) {
 	// TQt 1.x compat
 	*this = fromLatin1( "" );
-	return *this;
+    } else {
+	vsprintf(cformat, ap);
     }
 
-    TQString &s = vsprintf(cformat, ap);
-
     va_end(ap);
-    return s;
+    return *this;
 }
 
 TQString &TQString::vsprintf( const char* cformat, va_list ap )