numeric.c: use NUM2DBL
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59986 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
numeric.c: use NUM2DBL
NUM2DBL on unknown object. RFLOAT_VALUE is only appliicable to
T_FLOAT object. [ruby-core:82924] [Bug #13928]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59986 b2dd03c8-39d4-4d8f-98ff-823fe69b080e