Bug #34173425 Assertion failure: mtr0log.cc:NNN:n_inst > 0 thread NNN

Problem:
    read_2_bytes may return nullptr if ptr exceeds end_ptr. Any calls to
read_2_bytes must check if nullptr is returned.

Solution:
    Updated all instances where this check is required. Verified other
call sites as well

Change-Id: I5d9b2e737c94f83626b625342f36366838544021

storage/innobase/mtr/mtr0log.cc

@@ -1313,6 +1313,7 @@ static byte *parse_index_versioned_fields_8029(byte *ptr, const byte *end_ptr,
                                                size_t &n_dropped) {
   uint16_t n_inst = 0;
   ptr = read_2_bytes(ptr, end_ptr, n_inst);
+  if (ptr == nullptr) return (nullptr);
   ut_ad(n_inst > 0);
 
   for (auto i = n_inst; i > 0; --i) {