Drop redundant test with isnumchar

Fix pvs-studio error 'V501 There are identical sub-expressions
'(c) == '_'' to the left and to the right of the '||' operator.'. isnumchar()
is a macro defined as (nasm_isalnum(c) || (c) == '_')

Signed-off-by: Martin Lindhe <martin-commit@ubique.se>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

asm/preproc.c

@@ -1054,7 +1054,7 @@ static Token *tokenize(char *line)
                     is_float = true;
                     if (*p == '+' || *p == '-')
                         p++;
-                } else if (isnumchar(c) || c == '_')
+                } else if (isnumchar(c))
                     ; /* just advance */
                 else if (c == '.') {
                     /*