Get rid of some no-longer-necessary casts.

g_ascii_isXXX() can be handed a char value safely; they won't try to use
it as an index into a table before checking it.

Change-Id: Icf80163fb5f9dccd0b97917e318b1db0bf3e0cf8
Reviewed-on: https://code.wireshark.org/review/4801
Reviewed-by: Guy Harris <guy@alum.mit.edu>

capture_opts.c

@@ -258,7 +258,7 @@ set_autostop_criterion(capture_options *capture_opts, const char *autostoparg)
      * as we allow it in the preferences file, we might as well
      * allow it here).
      */
-    while (g_ascii_isspace((guchar)*p))
+    while (g_ascii_isspace(*p))
         p++;
     if (*p == '\0') {
         /*
@@ -309,7 +309,7 @@ get_ring_arguments(capture_options *capture_opts, const char *arg)
      * as we allow it in the preferences file, we might as well
      * allow it here).
      */
-    while (g_ascii_isspace((guchar)*p))
+    while (g_ascii_isspace(*p))
         p++;
     if (*p == '\0') {
         /*
@@ -355,7 +355,7 @@ get_sampling_arguments(capture_options *capture_opts, const char *arg)
     p = colonp;
     *p++ = '\0';
 
-    while (g_ascii_isspace((guchar)*p))
+    while (g_ascii_isspace(*p))
         p++;
     if (*p == '\0') {
         *colonp = ':';
@@ -413,7 +413,7 @@ get_auth_arguments(capture_options *capture_opts, const char *arg)
     p = colonp;
     *p++ = '\0';
 
-    while (g_ascii_isspace((guchar)*p))
+    while (g_ascii_isspace(*p))
         p++;
 
     if (capture_opts->ifaces->len > 0) {