iwl3945: do not send scan command if channel count zero

Do not send scan command if no channels to scan.

This avoids a Microcode error as reported in:
http://www.intellinuxwireless.org/bugzilla/show_bug.cgi?id=1650
http://bugzilla.kernel.org/show_bug.cgi?id=11806
http://marc.info/?l=linux-wireless&m=122437145211886&w=2

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl3945-base.c

@@ -6256,6 +6256,11 @@ static void iwl3945_bg_request_scan(struct work_struct *data)
 					      n_probes,
 			(void *)&scan->data[le16_to_cpu(scan->tx_cmd.len)]);
 
+	if (scan->channel_count == 0) {
+		IWL_DEBUG_SCAN("channel count %d\n", scan->channel_count);
+		goto done;
+	}
+
 	cmd.len += le16_to_cpu(scan->tx_cmd.len) +
 	    scan->channel_count * sizeof(struct iwl3945_scan_channel);
 	cmd.data = scan;