cleanup: add Item::convert_time_to_datetime() helper

will be used in following commits

sql/item.cc

@@ -151,13 +151,9 @@ bool Item::get_date_with_conversion(MYSQL_TIME *ltime, ulonglong fuzzydate)
   if (get_date(ltime, fuzzydate | time_flag))
     return true;
   if (ltime->time_type == MYSQL_TIMESTAMP_TIME &&
-      !(fuzzydate & TIME_TIME_ONLY))
-  {
-    MYSQL_TIME tmp;
-    if (time_to_datetime_with_warn(thd, ltime, &tmp, fuzzydate))
-      return null_value= true;
-    *ltime= tmp;
-  }
+      !(fuzzydate & TIME_TIME_ONLY) &&
+      convert_time_to_datetime(thd, ltime, fuzzydate))
+    return true;
   return false;
 }
 

sql/item.h

@@ -27,6 +27,7 @@
 #include "sql_const.h"                 /* RAND_TABLE_BIT, MAX_FIELD_NAME */
 #include "field.h"                              /* Derivation */
 #include "sql_type.h"
+#include "sql_time.h"
 
 C_MODE_START
 #include <ma_dyncol.h>
@@ -1361,6 +1362,14 @@ class Item: public Value_source,
   bool get_time(MYSQL_TIME *ltime)
   { return get_date(ltime, TIME_TIME_ONLY | TIME_INVALID_DATES); }
   // Get date with automatic TIME->DATETIME conversion
+  bool convert_time_to_datetime(THD *thd, MYSQL_TIME *ltime, ulonglong fuzzydate)
+  {
+    MYSQL_TIME tmp;
+    if (time_to_datetime_with_warn(thd, ltime, &tmp, fuzzydate))
+      return null_value= true;
+    *ltime= tmp;
+    return false;
+  }
   bool get_date_with_conversion(MYSQL_TIME *ltime, ulonglong fuzzydate);
   /*
     Get time with automatic DATE/DATETIME to TIME conversion.