Fix a signed/unsigned warning by using an unsigned int to compare against the result of sizeof(). bug 114241, r=bbaetz, sr=shaver.

xpcom/typelib/xpt/src/xpt_struct.c

@@ -174,7 +174,7 @@ XPT_PUBLIC_API(PRBool)
 XPT_DoHeaderPrologue(XPTArena *arena, XPTCursor *cursor, XPTHeader **headerp, PRUint32 * ide_offset)
 {
     XPTMode mode = cursor->state->mode;
-    int i;
+    unsigned int i;
     XPTHeader * header;
 
     if (mode == XPT_DECODE) {