* vm_insnhelper.c (vm_throw_start): check if the iseq is symbol
	  proc, class definition should not be a symbol proc.
	  [ruby-core:75856] [Bug #12462]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@55774 b2dd03c8-39d4-4d8f-98ff-823fe69b080e