chore: code cleanup, properly scope rpcWrapper context detach (#6481)

This is a very small code change that correctly scopes a context detach
call. Technically this could be considered a "fix", but it very unlikely
to matter in practice given that session.getExecutionContext.open() is
unlikely to fail.

server/src/main/java/io/deephaven/server/session/SessionServiceGrpcImpl.java

@@ -508,9 +508,9 @@ private static <ReqT, RespT> void rpcWrapper(
                 // Indicates a very serious failure; debateable whether we should even try to send close.
                 safeClose(call, Status.INTERNAL, new Metadata(), false);
                 throw error;
-            } finally {
-                context.detach(previous);
             }
+        } finally {
+            context.detach(previous);
         }
     }