Fix out of bounds array access on invalid macro arg references

A reference to an invalid macro argument (\ not followed by a digit
between 1 and 9) will cause an access outside of the bounds of the
currentmacroargs array in sym_FindMacroArg().

Macro arg references are processed in two places:

In CopyMacroArg(): called when scanning tokens between "", {} and
arguments of a macro call. The only problem here is that it accepts \0
as valid and so calls sym_FindMacroArg with a invalid value.

In PutMacroArg(): called by the lexer automata when it encounters a
token matching \\[0-9]? (in other cases than above). So not only it
accepts \0 but also \ alone.
  Memo: In setuplex(), a rule is defined with a regex composed of up to
    three ranges of chars and takes the form:
      [FirstRange]
      or [FirstRange][SecondRange]?
      or [FirstRange]([SecondRange][Range]*)?
    On scanning, when several rules match, the first longuest one is
    choosen.

Regression test:
1)
SECTION "HOME", HOME
	db "\0"

2)
SECTION "HOME", HOME
	db \A

3)
SECTION "HOME", HOME
	db \

src/asm/globlex.c

@@ -208,10 +208,14 @@ PutMacroArg(char *src, ULONG size)
 	char *s;
 
 	yyskipbytes(size);
-	if ((s = sym_FindMacroArg(src[1] - '0')) != NULL) {
+	if ((size == 2 && src[1] >= '1' && src[1] <= '9')) {
-		yyunputstr(s);
+		if ((s = sym_FindMacroArg(src[1] - '0')) != NULL) {
+			yyunputstr(s);
+		} else {
+			yyerror("Macro argument not defined");
+		}
 	} else {
-		yyerror("Macro argument not defined");
+		yyerror("Invalid macro argument");
 	}
 	return (0);
 }
@@ -387,7 +391,7 @@ setuplex(void)
 
 	    id = lex_FloatAlloc(&tMacroArgToken);
 	lex_FloatAddFirstRange(id, '\\', '\\');
-	lex_FloatAddSecondRange(id, '0', '9');
+	lex_FloatAddSecondRange(id, '1', '9');
 	id = lex_FloatAlloc(&tMacroUniqueToken);
 	lex_FloatAddFirstRange(id, '\\', '\\');
 	lex_FloatAddSecondRange(id, '@', '@');

src/asm/lexer.c

@@ -437,7 +437,6 @@ CopyMacroArg(char *dest, size_t maxLength, char c)
 	int argNum;
 	
 	switch (c) {
-	case '0':
 	case '1':
 	case '2':
 	case '3':