Bug#58022 ... like ... escape export_set ( ... ) crashes when export_set returns warnings

ESCAPE argument might be empty string. It leads
to server crash under some circumstances.
The fix:
-added check if ESCAPE argument result is not empty string

mysql-test/r/ctype_latin1.result:
  test case
mysql-test/t/ctype_latin1.test:
  test case
sql/item_cmpfunc.cc:
  -added check if ESCAPE argument result is not empty string

mysql-test/r/ctype_latin1.result

@@ -409,3 +409,11 @@ select hex(cast(_ascii 0x7f as char(1) character set latin1));
 hex(cast(_ascii 0x7f as char(1) character set latin1))
 7F
 End of 5.0 tests
+#
+# Bug#58022 ... like ... escape export_set ( ... ) crashes when export_set returns warnings
+#
+SELECT '' LIKE '' ESCAPE EXPORT_SET(1, 1, 1, 1, '');
+'' LIKE '' ESCAPE EXPORT_SET(1, 1, 1, 1, '')
+1
+Warnings:
+Warning	1292	Truncated incorrect INTEGER value: ''

mysql-test/t/ctype_latin1.test

@@ -127,3 +127,8 @@ DROP TABLE `abc
 select hex(cast(_ascii 0x7f as char(1) character set latin1));
 
 --echo End of 5.0 tests
+
+--echo #
+--echo # Bug#58022 ... like ... escape export_set ( ... ) crashes when export_set returns warnings
+--echo #
+SELECT '' LIKE '' ESCAPE EXPORT_SET(1, 1, 1, 1, '');

sql/item_cmpfunc.cc

@@ -4692,6 +4692,7 @@ bool Item_func_like::fix_fields(THD *thd, Item **ref)
     String *escape_str= escape_item->val_str(&cmp.value1);
     if (escape_str)
     {
+      const char *escape_str_ptr= escape_str->ptr();
       if (escape_used_in_parsing && (
              (((thd->variables.sql_mode & MODE_NO_BACKSLASH_ESCAPES) &&
                 escape_str->numchars() != 1) ||
@@ -4706,9 +4707,9 @@ bool Item_func_like::fix_fields(THD *thd, Item **ref)
         CHARSET_INFO *cs= escape_str->charset();
         my_wc_t wc;
         int rc= cs->cset->mb_wc(cs, &wc,
-                                (const uchar*) escape_str->ptr(),
-                                (const uchar*) escape_str->ptr() +
-                                               escape_str->length());
+                                (const uchar*) escape_str_ptr,
+                                (const uchar*) escape_str_ptr +
+                                escape_str->length());
         escape= (int) (rc > 0 ? wc : '\\');
       }
       else
@@ -4725,13 +4726,13 @@ bool Item_func_like::fix_fields(THD *thd, Item **ref)
         {
           char ch;
           uint errors;
-          uint32 cnvlen= copy_and_convert(&ch, 1, cs, escape_str->ptr(),
+          uint32 cnvlen= copy_and_convert(&ch, 1, cs, escape_str_ptr,
                                           escape_str->length(),
                                           escape_str->charset(), &errors);
           escape= cnvlen ? ch : '\\';
         }
         else
-          escape= *(escape_str->ptr());
+          escape= escape_str_ptr ? *escape_str_ptr : '\\';
       }
     }
     else