gdbstub: Fix double close() of the follow-fork-mode socket

When the terminal GDB_FORK_ENABLED state is reached, the coordination
socket is not needed anymore and is therefore closed. However, if there
is a communication error between QEMU gdbstub and GDB, the generic
error handling code attempts to close it again.

Fix by closing it later - before returning - instead.

Fixes: Coverity CID 1539966
Fixes: d547e71 ("gdbstub: Implement follow-fork-mode child")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240312001813.13720-1-iii@linux.ibm.com>

gdbstub/user.c

@@ -517,6 +517,7 @@ void gdbserver_fork_end(CPUState *cpu, pid_t pid)
         switch (gdbserver_user_state.fork_state) {
         case GDB_FORK_ENABLED:
             if (gdbserver_user_state.running_state) {
+                close(fd);
                 return;
             }
             QEMU_FALLTHROUGH;
@@ -542,7 +543,6 @@ void gdbserver_fork_end(CPUState *cpu, pid_t pid)
                 gdbserver_user_state.fork_state = GDB_FORK_ACTIVE;
                 break;
             case GDB_FORK_ENABLE:
-                close(fd);
                 gdbserver_user_state.fork_state = GDB_FORK_ENABLED;
                 break;
             case GDB_FORK_DISABLE:
@@ -557,7 +557,6 @@ void gdbserver_fork_end(CPUState *cpu, pid_t pid)
             if (write(fd, &b, 1) != 1) {
                 goto fail;
             }
-            close(fd);
             gdbserver_user_state.fork_state = GDB_FORK_ENABLED;
             break;
         case GDB_FORK_DISABLING: