Protect part of emitMetrics from panic behavior during post-seal

changelog/10708.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+metrics: Protect emitMetrics from panicking during post-seal
+```

vault/core_metrics.go

@@ -256,6 +256,13 @@ type kvMount struct {
 func (c *Core) findKvMounts() []*kvMount {
 	mounts := make([]*kvMount, 0)
 
+	// emitMetrics doesn't grab the statelock, so this code might run during or after the seal process.
+	// Therefore, we need to check if c.mounts is nil. If we do not, emitMetrics will panic if this is
+	// run after seal.
+	if c.mounts == nil {
+		return mounts
+	}
+
 	c.mountsLock.RLock()
 	defer c.mountsLock.RUnlock()