Bug#57818 string conversion function died

Bug#57913 large negative number to string conversion functions crash
String object which is used as result container of the item
has uninitialized 'str_charset' field. This object
might be used later to preform some internal operations
and str_charset field is involved in these operations.
It leads to crash.
The fix is to intialize str_charset in my_decimal2string() func.

mysql-test/r/func_str.result

@@ -2600,4 +2600,16 @@ ORDER BY QUOTE(t1.a);
 1
 1
 DROP TABLE t1;
+#
+# Bug#57913 large negative number to string conversion functions crash
+# Bug#57810 case/when/then : Assertion failed: length || !scale
+#
+SELECT '1' IN ('1', SUBSTRING(-9223372036854775809, 1));
+'1' IN ('1', SUBSTRING(-9223372036854775809, 1))
+1
+SELECT CONVERT(('' IN (REVERSE(CAST(('') AS DECIMAL)), '')), CHAR(3));
+CONVERT(('' IN (REVERSE(CAST(('') AS DECIMAL)), '')), CHAR(3))
+1
+Warnings:
+Warning	1292	Truncated incorrect DECIMAL value: ''
 End of 5.1 tests

mysql-test/t/func_str.test

@@ -1362,4 +1362,11 @@ SELECT 1 FROM t1, t1 t2
 ORDER BY QUOTE(t1.a);
 DROP TABLE t1;
 
+--echo #
+--echo # Bug#57913 large negative number to string conversion functions crash
+--echo # Bug#57810 case/when/then : Assertion failed: length || !scale
+--echo #
+SELECT '1' IN ('1', SUBSTRING(-9223372036854775809, 1));
+SELECT CONVERT(('' IN (REVERSE(CAST(('') AS DECIMAL)), '')), CHAR(3));
+
 --echo End of 5.1 tests

sql/my_decimal.cc

@@ -109,6 +109,7 @@ int my_decimal2string(uint mask, const my_decimal *d,
   result= decimal2string((decimal_t*) d, (char*) str->ptr(),
                          &length, (int)fixed_prec, fixed_dec,
                          filler);
+  str->set_charset(&my_charset_bin);
   str->length(length);
   return check_result(mask, result);
 }