more const in format detection

BaseImporter::SearchFileHeaderForToken() expected a pointer to a non-const token list. This was probably an oversight, as nobody would realistically expect the function to change the list. Furthermore, it prevented token lists from being compiled to read-only memory, in some cases even causing the compiler to generate thread-safe initialization.

The list is now const and all callers declare their token lists static const, thus compiling them to read-only memory.

code/AssetLib/MMD/MMDImporter.cpp

@@ -94,8 +94,8 @@ bool MMDImporter::CanRead(const std::string &pFile, IOSystem *pIOHandler,
         return SimpleExtensionCheck(pFile, "pmx");
     } else {
         // Check file Header
-        static const char *pTokens[] = { "PMX " };
-        return BaseImporter::SearchFileHeaderForToken(pIOHandler, pFile, pTokens, 1);
+        static const char * const pTokens[] = { "PMX " };
+        return SearchFileHeaderForToken(pIOHandler, pFile, pTokens, 1);
     }
 }