Avoid crash on NULL pointer in lock driver impls during hotplug

When virLockDriverAcquire is invoked during hotplug the state
parameter will be left as NULL.

* src/locking/lock_driver_nop.c,
  src/locking/lock_driver_sanlock.c: Don't reference NULL state
  parameter

src/locking/lock_driver_nop.c

@@ -76,6 +76,7 @@ static int virLockManagerNopRelease(virLockManagerPtr lock ATTRIBUTE_UNUSED,
                                     char **state,
                                     unsigned int flags ATTRIBUTE_UNUSED)
 {
+    if (state)
         *state = NULL;
 
     return 0;
@@ -85,7 +86,7 @@ static int virLockManagerNopInquire(virLockManagerPtr lock ATTRIBUTE_UNUSED,
                                     char **state,
                                     unsigned int flags ATTRIBUTE_UNUSED)
 {
-
+    if (state)
         *state = NULL;
 
     return 0;

src/locking/lock_driver_sanlock.c

@@ -374,6 +374,7 @@ static int virLockManagerSanlockRelease(virLockManagerPtr lock,
 
     virCheckFlags(0, -1);
 
+    if (state) {
         if ((rv = sanlock_inquire(-1, priv->vm_pid, 0, &res_count, state)) < 0) {
             if (rv <= -200)
                 virLockError(VIR_ERR_INTERNAL_ERROR,
@@ -386,6 +387,7 @@ static int virLockManagerSanlockRelease(virLockManagerPtr lock,
 
         if (STREQ(*state, ""))
             VIR_FREE(*state);
+    }
 
     if ((rv = sanlock_release(-1, priv->vm_pid, SANLK_REL_ALL, 0, NULL)) < 0) {
         if (rv <= -200)
@@ -409,6 +411,11 @@ static int virLockManagerSanlockInquire(virLockManagerPtr lock,
 
     virCheckFlags(0, -1);
 
+    if (!state) {
+        virLockError(VIR_ERR_INVALID_ARG, "state");
+        return -1;
+    }
+
     VIR_DEBUG("pid=%d", priv->vm_pid);
 
     if ((rv = sanlock_inquire(-1, priv->vm_pid, 0, &res_count, state)) < 0) {