~FramedSource(): Don't throw an exception if the remote has disconnected

This would cause the daemon to crash with a call to terminate().

src/libutil/serialise.hh

@@ -483,6 +483,7 @@ struct FramedSource : Source
 
     ~FramedSource()
     {
+        try {
             if (!eof) {
                 while (true) {
                     auto n = readInt(from);
@@ -491,6 +492,9 @@ struct FramedSource : Source
                     from(data.data(), n);
                 }
             }
+        } catch (...) {
+            ignoreException();
+        }
     }
 
     size_t read(char * data, size_t len) override