[uri] Handle an empty unparse_uri() result properly

Previously, if none of the URI parts requested existed in the passed
URI, unparse_uri() would not touch the destination buffer at all; this
could lead to use of uninitialized data. Fix by setting buf[0] = '\0'
before unparsing whenever we have room to do so.

Signed-off-by: Joshua Oreman <oremanj@rwcr.net>
Signed-off-by: Marty Connor <mdc@etherboot.org>

src/core/uri.c

@@ -225,12 +225,13 @@ int unparse_uri ( char *buf, size_t size, struct uri *uri,
 	dump_uri ( uri );
 	DBG ( "\n" );
 
+	/* Ensure buffer is NUL-terminated */
+	if ( size )
+		buf[0] = '\0';
+
 	/* Special-case NULL URI */
-	if ( ! uri ) {
-		if ( size )
-			buf[0] = '\0';
+	if ( ! uri )
 		return 0;
-	}
 
 	/* Iterate through requested fields */
 	for ( i = URI_FIRST_FIELD; i <= URI_LAST_FIELD; i++ ) {