MDEV-5404 Can't free data returned by mariadb_dyncol_unpack on windows

add mariadb_dyncol_unpack_free()

include/ma_dyncol.h

@@ -220,6 +220,9 @@ mariadb_dyncol_unpack(DYNAMIC_COLUMN *str,
                       uint *count,
                       MYSQL_LEX_STRING **names, DYNAMIC_COLUMN_VALUE **vals);
 
+void mariadb_dyncol_unpack_free(MYSQL_LEX_STRING *names,
+                                DYNAMIC_COLUMN_VALUE *vals);
+
 int mariadb_dyncol_column_cmp_named(const MYSQL_LEX_STRING *s1,
                                     const MYSQL_LEX_STRING *s2);
 

libmysql/CMakeLists.txt

@@ -248,6 +248,7 @@ mariadb_dyncol_val_str
 mariadb_dyncol_val_long
 mariadb_dyncol_val_double
 mariadb_dyncol_unpack
+mariadb_dyncol_unpack_free
 mariadb_dyncol_column_cmp_named
 mariadb_dyncol_column_count
 mariadb_dyncol_prepare_decimal

mysys/ma_dyncol.c

@@ -4316,6 +4316,18 @@ mariadb_dyncol_unpack(DYNAMIC_COLUMN *str,
   return rc;
 }
 
+/**
+  Free arrays allocated by mariadb_dyncol_unpack()
+
+  @param names           Where to put names (should be free by user)
+  @param vals            Where to put values (should be free by user)
+*/
+void mariadb_dyncol_unpack_free(LEX_STRING *names, DYNAMIC_COLUMN_VALUE *vals)
+{
+  my_free(names);
+  my_free(vals);
+}
+
 /**
   Get not NULL column count
 

storage/cassandra/ha_cassandra.cc

@@ -1925,16 +1925,9 @@ int ha_cassandra::write_dynamic_row(uint count,
 void ha_cassandra::free_dynamic_row(DYNAMIC_COLUMN_VALUE **vals,
                                     LEX_STRING **names)
 {
-  if (*vals)
-  {
-    my_free(*vals);
-    *vals= 0;
-  }
-  if (*names)
-  {
-    my_free(*names);
-    *names= 0;
-  }
+  mariadb_dyncol_unpack_free(*names, *vals);
+  *vals= 0;
+  *names= 0;
 }
 
 int ha_cassandra::write_row(uchar *buf)