BUG#11908153 CRASH AND/OR VALGRIND ERRORS IN FIELD_BLOB::GET_KEY_IMAGE

Backporting bug patch from 5.5 to 5.1.
This fix is applicable to BUG#14362617 as well

sql/field.h

@@ -1824,7 +1824,13 @@ public:
   int  store(longlong nr, bool unsigned_val);
   int  store_decimal(const my_decimal *);
   uint size_of() const { return sizeof(*this); }
-  int  reset(void) { return !maybe_null() || Field_blob::reset(); }
+
+  /**
+    Non-nullable GEOMETRY types cannot have defaults,
+    but the underlying blob must still be reset.
+   */
+  int reset(void) { return Field_blob::reset() || !maybe_null(); }
+
   geometry_type get_geometry_type() { return geom_type; };
 };
 #endif /*HAVE_SPATIAL*/

sql/field_conv.cc

@@ -179,7 +179,10 @@ set_field_to_null_with_conversions(Field *field, bool no_conversions)
     ((Field_timestamp*) field)->set_time();
     return 0;					// Ok to set time to NULL
   }
+  
+  // Note: we ignore any potential failure of reset() here.
   field->reset();
+
   if (field == field->table->next_number_field)
   {
     field->table->auto_increment_field_not_null= FALSE;