AppModel: Don't crash on MetadataUsage MethodDef/Ref without prior method definition

Il2CppInspector.Common/Model/AppModel.cs

@@ -211,6 +211,12 @@ namespace Il2CppInspector.Model
                             declarationGenerator.IncludeMethod(method);
                             AddTypes(declarationGenerator.GenerateRemainingTypeDeclarations());
                             
+                            // Any method here SHOULD already be in the Methods list
+                            // but we have seen one example where this is not the case for a MethodDef
+                            if (!Methods.ContainsKey(method)) {
+                                var fnPtr = declarationGenerator.GenerateMethodDeclaration(method);
+                                Methods.Add(method, fnPtr, new AppMethod(method, fnPtr) {Group = Group});
+                            }
                             Methods[method].MethodInfoPtrAddress = address;
                             break;
                     }