numeric.c: fix infinite loop

	* numeric.c (int_pow): fix infinite loop in the case of y equal 1
	  and power of x does not overflow.
	  [ruby-core:91734] [Bug #15651]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_6@67222 b2dd03c8-39d4-4d8f-98ff-823fe69b080e