[lldb] [Mach-O] don't strip the end of the "kern ver str" LC_NOTE (#77538)

The "kern ver str" LC_NOTE gives lldb a kernel version string -- with a
UUID and/or a load address (stext) to load it at. The LC_NOTE specifies
a size of the identifier string in bytes. In
ObjectFileMachO::GetIdentifierString, I copy that number of bytes into a
std::string, and in case there were additional nul characters at the end
of the sting for padding reasons, I tried to shrink the std::string to
not include these extra nul's.

However, I did this resizing without handling the case of an empty
identifier string. I don't know why any corefile creator would do that,
but of course at least one does. This patch removes the resizing
altogether; I was solving something that hasn't ever shown to be a
problem. I also added a test case for this, to check that lldb doesn't
crash when given one of these corefiles.

rdar://120390199

lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp

@@ -5467,8 +5467,6 @@ std::string ObjectFileMachO::GetIdentifierString() {
           uint32_t strsize = payload_size - sizeof(uint32_t);
           std::string result(strsize, '\0');
           m_data.CopyData(payload_offset, strsize, result.data());
-          while (result.back() == '\0')
-            result.resize(result.size() - 1);
           LLDB_LOGF(log, "LC_NOTE 'kern ver str' found with text '%s'",
                     result.c_str());
           return result;
@@ -5488,8 +5486,6 @@ std::string ObjectFileMachO::GetIdentifierString() {
         std::string result(ident_command.cmdsize, '\0');
         if (m_data.CopyData(offset, ident_command.cmdsize, result.data()) ==
             ident_command.cmdsize) {
-          while (result.back() == '\0')
-            result.resize(result.size() - 1);
           LLDB_LOGF(log, "LC_IDENT found with text '%s'", result.c_str());
           return result;
         }