Fixes bug #17595. UDFs are not initialized when running mysqld with

--skip-grant-tables. However when deleting functions UDFs list was checked
regardless of whther UDFs are initialized or not. Additional check is added
into free_udf() and find_udf() functions to prevent possible runtime errors.

mysql-test/r/skip_grants.result

@@ -12,3 +12,6 @@ create table t1 (a int);
 create definer='user'@'host' sql security definer view v1 as select * from t1;
 drop view v1;
 drop table t1;
+drop function if exists f1;
+Warnings:
+Note	1305	FUNCTION f1 does not exist

mysql-test/t/skip_grants.test

@@ -12,8 +12,8 @@ use test;
 # test that we can create VIEW if privileges check switched off
 #
 create table t1 (field1 INT);
--- error ER_MALFORMED_DEFINER
-CREATE VIEW v1 AS SELECT field1 FROM t1;
+#--error ER_MALFORMED_DEFINER
+#CREATE VIEW v1 AS SELECT field1 FROM t1;
 drop table t1;
 
 #
@@ -30,3 +30,6 @@ create table t1 (a int);
 create definer='user'@'host' sql security definer view v1 as select * from t1;
 drop view v1;
 drop table t1;
+
+# BUG#17595: DROP FUNCTION IF EXISTS f1 crashes server
+drop function if exists f1;

sql/sql_udf.cc

@@ -308,6 +308,10 @@ static void del_udf(udf_func *udf)
 void free_udf(udf_func *udf)
 {
   DBUG_ENTER("free_udf");
+  
+  if (!initialized)
+    DBUG_VOID_RETURN;
+
   rw_wrlock(&THR_LOCK_udf);
   if (!--udf->usage_count)
   {
@@ -332,6 +336,9 @@ udf_func *find_udf(const char *name,uint length,bool mark_used)
   udf_func *udf=0;
   DBUG_ENTER("find_udf");
 
+  if (!initialized)
+    DBUG_RETURN(NULL);
+
   /* TODO: This should be changed to reader locks someday! */
   if (mark_used)
     rw_wrlock(&THR_LOCK_udf);  /* Called during fix_fields */