rbutilqt/themeeditor: Fix compiler warnings

- match sign in integer comparison
- remove unused RBViewport member

Co-authored-by: ChatGPT (GPT-5.3 Mini) <chatgpt@openai.com>
Change-Id: I9a59d701593a4290523bf4b837ab0794bea2ebaa

utils/rbutilqt/base/ttscarbon.cpp

@@ -328,7 +328,7 @@ int TTSCarbon::convertAiffToWav(const char* aiff, const char* wav)
     if(!buf) /* error out if malloc() failed */
         return -1;
     in = fopen(aiff, "rb");
-    if(fread(buf, 1, filestat.st_size, in) < filestat.st_size) {
+    if(fread(buf, 1, filestat.st_size, in) < (size_t)filestat.st_size) {
         printf("could not read file: not enought bytes read\n");
         fclose(in);
         free(buf);

utils/themeeditor/graphics/rbviewport.h

@@ -119,8 +119,6 @@ private:
     int baseParam;
     ParseTreeNode* node;
     SkinDocument* doc;
-
-    bool mirrored;
 };
 
 #endif // RBVIEWPORT_H