Fix optional argument parsing

As `optional` does not backtrack, the parser would get stuck in its ways
if it could parse spaces after an instruction without any argument:
```
NOT    ; Comment
```
An explicit try was added to backtrack and not fail the parse.

src/Mima/Asm/Phase1/Parse.hs

@@ -114,7 +114,7 @@ instruction = small <|> large
       stop <- getOffset
       pure $ LargeInstruction (Span start stop) lo sv
     optionalAwareArgument (LargeOpcode _ code)
-      | Vm.argumentIsOptional code = optional (inlineSpace1 *> smallValue <?> "argument")
+      | Vm.argumentIsOptional code = optional $ try (inlineSpace1 *> smallValue <?> "argument")
       | otherwise                  = Just <$> (inlineSpace1 *> smallValue <?> "argument")
 
 singleDirective