fix windows build

sql/field.cc

@@ -6412,7 +6412,7 @@ void Field_varstring::sql_type(String &res) const
 }
 
 
-uint Field_varstring::data_length(const char *from)
+uint32 Field_varstring::data_length(const char *from)
 {
   return length_bytes == 1 ? (uint) (uchar) *ptr : uint2korr(ptr);
 }

sql/field.h

@@ -1107,7 +1107,7 @@ public:
   int key_cmp(const byte *str, uint length);
   uint packed_col_length(const char *to, uint length);
   uint max_packed_col_length(uint max_length);
-  uint data_length(const char *from);
+  uint32 data_length(const char *from);
   uint size_of() const { return sizeof(*this); }
   enum_field_types real_type() const { return MYSQL_TYPE_VARCHAR; }
   bool has_charset(void) const