chore: make sure xmodel flags are unsigned

src/Common/Game/IW3/IW3_Assets.h

@@ -530,7 +530,7 @@ namespace IW3
         int16_t collLod;
         XModelStreamInfo streamInfo;
         int memUsage;
-        char flags;
+        unsigned char flags;
         bool bad;
         PhysPreset* physPreset;
         PhysGeomList* physGeoms;

src/Common/Game/IW4/IW4_Assets.h

@@ -586,7 +586,7 @@ namespace IW4
         char maxLoadedLod;
         unsigned char numLods;
         char collLod;
-        char flags;
+        unsigned char flags;
         XModelCollSurf_s* collSurfs;
         int numCollSurfs;
         int contents;