pour_bottle?: Pour local bottles without sha256

Pouring a local bottle for a formula without a bottle sha256
in the formula for that OS would unexpectedly install from
source instead.

Library/Homebrew/formula_installer.rb

@@ -85,7 +85,7 @@ class FormulaInstaller
     return false if @pour_failed
 
     bottle = formula.bottle
-    return false unless bottle
+    return false if !bottle && !formula.local_bottle_path
     return true  if force_bottle?
     return false if build_from_source? || build_bottle? || interactive?
     return false if ARGV.cc