[rubygems/rubygems] Fix Kernel#warn override to handle backtrace location with nil path

It's very unlikely to hit this case, but it is possible, as
Thread::Backtrace::Location#path can return nil if the location is
a cfunc with no previous iseq.  See location_path in vm_backtrace.c
in Ruby.

https://github.com/rubygems/rubygems/commit/511935645a

1 files changed, 5 insertions, 4 deletions

diff --git a/lib/rubygems/core_ext/kernel_warn.rb b/lib/rubygems/core_ext/kernel_warn.rb
index e10a845b98..e030ef815c 100644
--- a/lib/rubygems/core_ext/kernel_warn.rb
+++ b/lib/rubygems/core_ext/kernel_warn.rb
@@ -38,10 +38,11 @@ if RUBY_VERSION >= "2.5"
 
           start += 1
 
-          path = loc.path
-          unless path.start_with?(rubygems_path) or path.start_with?('<internal:')
-            # Non-rubygems frames
-            uplevel -= 1
+          if path = loc.path
+            unless path.start_with?(rubygems_path) or path.start_with?('<internal:')
+              # Non-rubygems frames
+              uplevel -= 1
+            end
           end
         end
         uplevel = start