Properly cache shared flow node types

Author: ahejlsberg

src/compiler/checker.ts

@@ -21726,6 +21726,7 @@ namespace ts {
                     return errorType;
                 }
                 flowDepth++;
+                let sharedFlow: FlowNode | undefined;
                 while (true) {
                     const flags = flow.flags;
                     if (flags & FlowFlags.Shared) {
@@ -21738,6 +21739,7 @@ namespace ts {
                                 return sharedFlowTypes[i];
                             }
                         }
+                        sharedFlow = flow;
                     }
                     let type: FlowType | undefined;
                     if (flags & FlowFlags.Assignment) {
@@ -21801,9 +21803,9 @@ namespace ts {
                         // simply return the non-auto declared type to reduce follow-on errors.
                         type = convertAutoToAny(declaredType);
                     }
-                    if (flags & FlowFlags.Shared) {
+                    if (sharedFlow) {
                         // Record visited node and the associated type in the cache.
-                        sharedFlowNodes[sharedFlowCount] = flow;
+                        sharedFlowNodes[sharedFlowCount] = sharedFlow;
                         sharedFlowTypes[sharedFlowCount] = type;
                         sharedFlowCount++;
                     }