fix(fromFetch): don't abort if fetch resolves

Closes#4739

Author: cartant

src/internal/observable/dom/fetch.ts

@@ -55,6 +55,7 @@ export function fromFetch(input: string | Request, init?: RequestInit): Observab
 constcontroller=newAbortController();
 constsignal=controller.signal;
 letouterSignalHandler: ()=>void;
+letabortable=true;
 letunsubscribed=false;
 
 if(init){
@@ -73,9 +74,11 @@ export function fromFetch(input: string | Request, init?: RequestInit): Observab
 }
 
 fetch(input,init).then(response=>{
+abortable=false;
 subscriber.next(response);
 subscriber.complete();
 }).catch(err=>{
+abortable=false;
 if(!unsubscribed){
 // Only forward the error if it wasn't an abort.
 subscriber.error(err);
@@ -84,7 +87,9 @@ export function fromFetch(input: string | Request, init?: RequestInit): Observab
 
 return()=>{
 unsubscribed=true;
-controller.abort();
+if(abortable){
+controller.abort();
+}
 };
 });
 }