libdpkg: Refactor string termination in path_quote_filename

Move all destination string termination to the end of the function.
Always check the size limit before writting to the desintation and bail
out if there's no enough space.

lib/dpkg/path.c

@@ -3,7 +3,7 @@
  * path.c - path handling functions
  *
  * Copyright © 1995 Ian Jackson <ian@chiark.greenend.org.uk>
- * Copyright © 2008, 2009 Guillem Jover <guillem@debian.org>
+ * Copyright © 2008-2010 Guillem Jover <guillem@debian.org>
  *
  * This is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -113,39 +113,34 @@ path_quote_filename(char *dst, const char *src, size_t n)
 	if (size == 0)
 		return r;
 
-	while (size > 0) {
-		if (*src == '\0') {
-			*dst = '\0';
-			return r;
-		} else if (*src == '\\') {
-			if (size <= 2) {
-				/* Buffer full. */
-				*dst = '\0';
-				return r;
-			}
+	while (*src) {
+		if (*src == '\\') {
+			size -= 2;
+			if (size <= 0)
+				break;
+
 			*dst++ = '\\';
 			*dst++ = '\\';
 			src++;
-			size -= 2;
 		} else if (((*src) & 0x80) == '\0') {
+			size--;
+			if (size <= 0)
+				break;
+
 			*dst++ = *src++;
-			--size;
 		} else {
-			if (size > 4) {
-				sprintf(dst, "\\%03o",
-				        *(const unsigned char *)src);
-				size -= 4;
-				dst += 4;
-				src++;
-			} else {
-				/* Buffer full. */
-				*dst = '\0';
-				return r;
-			}
+			size -= 4;
+			if (size <= 0)
+				break;
+
+			sprintf(dst, "\\%03o",
+			        *(const unsigned char *)src);
+			dst += 4;
+			src++;
 		}
 	}
-	/* Buffer full. */
-	*(dst - 1) = '\0';
+
+	*dst = '\0';
 
 	return r;
 }