message: Don't crash when disassembling an unknown SPIR-V extension operation
diff: @@ -1416,10 +1416,21 @@ struct SPVInstruction
  #if USE_CANONICAL_EXT_INST_NAMES
  ret += op->arguments[0]->ext->setname + "::";
  - ret += op->arguments[0]->ext->canonicalNames[op->literals[0]];
  + const char **names = op->arguments[0]->ext->canonicalNames;
  #else
  - ret += op->arguments[0]->ext->friendlyNames[op->literals[0]];
  + const char **names = op->arguments[0]->ext->friendlyNames;
  #endif
  + if(names)
  + {
  + ret += names[op->literals[0]];
  + }
  + else
  + {
  +#if !USE_CANONICAL_EXT_INST_NAMES
  + ret += op->arguments[0]->ext->setname + "::";
  +#endif
  + ret += StringFormat::Fmt("op%u", op->literals[0]);
  + }
  ret += "(";
  