HttpBinaryCacheStore::getFile(): Fix uncaught exception

This method is marked as `noexcept`, but `enqueueFileTransfer()` can
throw `Interrupted` if the user has hit Ctrl-C or if the `ThreadPool`
that the thread is a part of is shutting down.

(cherry picked from commit 4566854981)

src/libstore/http-binary-cache-store.cc

@@ -169,10 +169,6 @@ protected:
     {
         try {
             checkEnabled();
-        } catch (...) {
-            callback.rethrow();
-            return;
-        }
 
             auto request(makeRequest(path));
 
@@ -191,6 +187,11 @@ protected:
                         callbackPtr->rethrow();
                     }
             }});
+
+        } catch (...) {
+            callback.rethrow();
+            return;
+        }
     }
 
     /**