Fix file seeking of gba ROM and fix seeking behaviour of EMUFILE_FILE

desmume/src/addons/slot2_gbagame.cpp

@@ -60,6 +60,8 @@ private:
 	u32	readRom(const u32 pos, const u8 size) 
 	{
 		if (!fROM) return 0xFFFFFFFF;
+		
+		fROM->fseek(pos, SEEK_SET);
 	
 		u32 data = 0xFFFFFFFF;
 		u32 readed = fROM->fread(&data, size);

desmume/src/emufile.cpp

@@ -83,17 +83,19 @@ int EMUFILE_FILE::fseek(int offset, int origin)
 		{
 			if(mFilePosition == offset)
 			{
-				return mFilePosition;
+				return 0;
 			}
 		}
 	}
 
 	mCondition = eCondition_Clean;
 
-	int pos = ::fseek(fp, offset, origin);
-	mPositionCacheEnabled = pos;
-
-	return pos;
+	int ret = ::fseek(fp, offset, origin);
+ 
+	if(mPositionCacheEnabled)
+		mFilePosition = ::ftell(fp);
+ 
+	return ret;
 }