MDEV-26019: Upgrading MariaDB breaks TLS mariabackup SST

Fixed typo in variable name that breaks SST in some scenatios.

Also fixed one small inaccuracy after MDEV-25978 which leads
to the use of an uninitialized variable when the --log-bin
option is specified without an argument.

scripts/wsrep_sst_common.sh

@@ -456,7 +456,7 @@ if [ -n "${MYSQLD_OPT_LOG_BASENAME:-}" -a \
 fi
 
 # If the --log-bin option is present without a value, then
-# setting WSREP_SST_OPT_BINLOG by using other arguments:
+# set WSREP_SST_OPT_BINLOG value using other arguments:
 if [ -z "$WSREP_SST_OPT_BINLOG" -a -n "${MYSQLD_OPT_LOG_BIN+x}" ]; then
     if [ -n "$WSREP_SST_OPT_LOG_BASENAME" ]; then
         # If the WSREP_SST_OPT_BINLOG variable is not set, but
@@ -465,9 +465,8 @@ if [ -z "$WSREP_SST_OPT_BINLOG" -a -n "${MYSQLD_OPT_LOG_BIN+x}" ]; then
         # the "-bin" suffix:
         readonly WSREP_SST_OPT_BINLOG="$WSREP_SST_OPT_LOG_BASENAME-bin"
     else
-        # the default name, note that base of this name
-        # is already defined above
-        readonly WSREP_SST_OPT_BINLOG_INDEX="$WSREP_SST_OPT_BINLOG.index"
+        # Take the default name:
+        readonly WSREP_SST_OPT_BINLOG='mysql-bin'
     fi
 fi
 
@@ -550,8 +549,8 @@ get_binlog()
                 # the "-bin" suffix:
                 readonly WSREP_SST_OPT_BINLOG_INDEX="$WSREP_SST_OPT_LOG_BASENAME-bin.index"
             else
-                # the default name, note that base of this name
-                # is already defined above
+                # the default name (note that base of this name
+                # is already defined above):
                 readonly WSREP_SST_OPT_BINLOG_INDEX="$WSREP_SST_OPT_BINLOG.index"
             fi
         fi

scripts/wsrep_sst_mariabackup.sh

@@ -386,7 +386,7 @@ get_transfer()
                 elif is_local_ip "$WSREP_SST_OPT_HOST_UNESCAPED"; then
                     CN_option=',commonname=localhost'
                 else
-                    CN_option=",commonname='$WSREP_SST_OPT_HOST_UNSECAPED'"
+                    CN_option=",commonname='$WSREP_SST_OPT_HOST_UNESCAPED'"
                 fi
                 tcmd="$tcmd,cert='$tpem',key='$tkey',cafile='$tcert'$CN_option$sockopt"
                 wsrep_log_info "$action with cert=$tpem, key=$tkey, cafile=$tcert"