Bug #58695 mysqltest coredumps on "if($x == ){"

Add check that there is a RHS of the expression
Added to mysqltest.test

client/mysqltest.cc

@@ -5680,6 +5680,8 @@ void do_block(enum block_cmd cmd, struct st_command* command)
     }
     while (my_isspace(charset_info, *curr_ptr))
       curr_ptr++;
+    if (curr_ptr == expr_end)
+      die("Missing right operand in comparison");
 
     /* Strip off trailing white space */
     while (my_isspace(charset_info, expr_end[-1]))

mysql-test/r/mysqltest.result

@@ -434,6 +434,8 @@ anything goes
 mysqltest: At line 2: Only == and != are supported for string values
 mysqltest: At line 2: Found junk '~= 6' after $variable in condition
 mysqltest: At line 2: Expression in if/while must beging with $, ` or a number
+mysqltest: At line 1: Missing right operand in comparison
+mysqltest: At line 1: Missing right operand in comparison
 counter is 2
 counter is 3
 counter is 4

mysql-test/t/mysqltest.test

@@ -1354,6 +1354,11 @@ EOF
 --exec $MYSQL_TEST < $MYSQL_TMP_DIR/mysqltest.sql 2>&1
 remove_file $MYSQL_TMP_DIR/mysqltest.sql;
 
+--error 1
+--exec echo "if (\$var ==) {" | $MYSQL_TEST  2>&1
+--error 1
+--exec echo "if (\$var > ) {" | $MYSQL_TEST  2>&1
+
 # ----------------------------------------------------------------------------
 # Test while with compare conditions
 # ----------------------------------------------------------------------------