Avoid failing even if given path does not match with prefix

Author: namusyaka

CHANGELOG.md

@@ -8,6 +8,7 @@
 
 #### Fixes
 
+* [#1548](https://github.com/ruby-grape/grape/pull/1548): Avoid failing even if given path does not match with prefix - [@thomas-peyric](https://github.com/thomas-peyric), [@namusyaka](https://github.com/namusyaka).
 * Your contribution here.
 
 ### 0.19.0 (12/18/2016)

lib/grape/middleware/versioner/path.rb

@@ -26,7 +26,7 @@ def default_options
         def before
           path = env[Grape::Http::Headers::PATH_INFO].dup
 
-          if prefix && path.index(prefix).zero?
+          if prefix && path.index(prefix) == 0
             path.sub!(prefix, '')
             path = Grape::Router.normalize_path(path)
           end

spec/grape/middleware/versioner/path_spec.rb

@@ -41,4 +41,11 @@
       end
     end
   end
+
+  context 'with prefix, but requested version is not matched' do
+    let(:options) { { prefix: '/v1', pattern: /v./i } }
+    it 'recognizes potential version' do
+      expect(subject.call('PATH_INFO' => '/v3/foo').last).to eq('v3')
+    end
+  end
 end