Fix generation of multiple interfaces in C# for some edge cases.

src/Generator/Passes/MultipleInheritancePass.cs

@@ -83,6 +83,11 @@ namespace CppSharp.Passes
             if (@base.CompleteDeclaration != null)
                 @base = (Class) @base.CompleteDeclaration;
 
+            // Prevent multiple interfaces from being generated in cases of
+            // a secondary base being inherited multiple times in a chain.
+            if (@base.IsInterface)
+                return @base;
+
             return interfaces.FirstOrDefault(i => i.OriginalClass == @base) ??
                 GetNewInterface("I" + @base.Name, @base);
         }

src/Generator/Passes/ParamTypeToInterfacePass.cs

@@ -31,6 +31,10 @@ namespace CppSharp.Passes
             if (!base.VisitFunctionDecl(function))
                 return false;
 
+            // TODO: Fix this once Dispose methods are generated in a pass.
+            if (function.SynthKind == FunctionSynthKind.InterfaceDispose)
+                return false;
+
             // parameters and returns from a specialised interface
             // must not be replaced if the templated interface uses a template parameter
             var interfaceFunction = GetInterfaceFunction(function);
@@ -97,7 +101,7 @@ namespace CppSharp.Passes
             if (@class == null || !@class.IsInterface)
                 return null;
 
-            return @class.Methods.First(m => m.OriginalFunction == function.OriginalFunction);
+            return @class.Methods.FirstOrDefault(m => m.OriginalFunction == function.OriginalFunction);
         }
 
         private static Property GetTemplateInterfaceProperty(Property property)