Avoid crashing on unresolved dependencies (#70871)

Fixes #70815.

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/LazyGenerics/GraphBuilder.cs

@@ -201,8 +201,11 @@ private void WalkMethod(EcmaMethod method)
                                      && _metadataReader.GetMemberReference((MemberReferenceHandle)accessedMethod).Parent.Kind == HandleKind.TypeSpecification))
                             {
                                 var m = methodIL.GetObject(MetadataTokens.GetToken(accessedMethod), NotFoundBehavior.ReturnNull) as MethodDesc;
-                                ProcessTypeReference(m.OwningType, typeContext, methodContext);
-                                ProcessMethodCall(m, typeContext, methodContext);
+                                if (m != null)
+                                {
+                                    ProcessTypeReference(m.OwningType, typeContext, methodContext);
+                                    ProcessMethodCall(m, typeContext, methodContext);
+                                }
                             }
                             break;
 

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/UsageBasedMetadataManager.cs

@@ -683,13 +683,21 @@ private void GetFlowDependenciesForInstantiation(ref DependencyList dependencies
                 var genericParameter = (GenericParameterDesc)typicalInstantiation[i];
                 if (FlowAnnotations.GetGenericParameterAnnotation(genericParameter) != default)
                 {
-                    var deps = ILCompiler.Dataflow.ReflectionMethodBodyScanner.ProcessGenericArgumentDataFlow(factory, FlowAnnotations, Logger, genericParameter, instantiation[i], source);
-                    if (deps.Count > 0)
+                    try
                     {
-                        if (dependencies == null)
-                            dependencies = deps;
-                        else
-                            dependencies.AddRange(deps);
+                        var deps = ILCompiler.Dataflow.ReflectionMethodBodyScanner.ProcessGenericArgumentDataFlow(factory, FlowAnnotations, Logger, genericParameter, instantiation[i], source);
+                        if (deps.Count > 0)
+                        {
+                            if (dependencies == null)
+                                dependencies = deps;
+                            else
+                                dependencies.AddRange(deps);
+                        }
+                    }
+                    catch (TypeSystemException)
+                    {
+                        // Wasn't able to do dataflow because of missing references or something like that.
+                        // This likely won't compile either, so we don't care about missing dependencies.
                     }
                 }
             }