Explicitly test for the empty string in Channel_UserHasMode()

Basically this is unnecessary, as Channel_UserModes() always returns a
valid pointer and strchr() can deal with an empty (NULL-terminated)
string perfectly fine, bit it makes the code a bit more obvious and
silences the following warning:

  In function ‘Channel_UserHasMode’,
      inlined from ‘Channel_Kick’ at channel.c:384:7:
  channel.c:784:16: warning: ‘strchr’ reading 1 or more bytes from a region
                    of size 0 [-Wstringop-overread]
    784 |         return strchr(Channel_UserModes(Chan, Client), Mode) != NULL;
        |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This was seen with "gcc (Debian 12.2.0-14) 12.2.0" at least.

1 files changed, 19 insertions, 1 deletions

diff --git a/src/ngircd/channel.c b/src/ngircd/channel.c
index bf891863..9994e65f 100644
--- a/src/ngircd/channel.c
+++ b/src/ngircd/channel.c
@@ -778,10 +778,28 @@ Channel_UserModes( CHANNEL *Chan, CLIENT *Client )
 } /* Channel_UserModes */
 
 
+/**
+ * Test if a user has a given channel user mode.
+ *
+ * @param Chan The channel to check.
+ * @param Client The client to check.
+ * @param Mode The channel user mode to test for.
+ * @return true if the user has the given channel user mode set.
+ */
 GLOBAL bool
 Channel_UserHasMode( CHANNEL *Chan, CLIENT *Client, char Mode )
 {
-	return strchr(Channel_UserModes(Chan, Client), Mode) != NULL;
+	char *channel_user_modes;
+
+	assert(Chan != NULL);
+	assert(Client != NULL);
+	assert(Mode > 0);
+
+	channel_user_modes = Channel_UserModes(Chan, Client);
+	if (!channel_user_modes || !*channel_user_modes)
+		return false;
+
+	return strchr(channel_user_modes, Mode) != NULL;
 } /* Channel_UserHasMode */