daemon: fix temp file leak in do_vgmeta on error paths (#314)

When vgcfgbackup fails or subsequent file operations fail, the
temporary file created by mkstemp is never unlinked. Add unlink(tmp)
to all error paths after mkstemp to prevent temp files accumulating
in /tmp.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

daemon/lvm.c

@@ -771,6 +771,7 @@ do_vgmeta (const char *vg, size_t *size_r)
   r = command (NULL, &err, "lvm", "vgcfgbackup", "-f", tmp, vg, NULL);
   if (r == -1) {
     reply_with_error ("vgcfgbackup: %s", err);
+    unlink (tmp);
     return NULL;
   }
 
@@ -778,6 +779,7 @@ do_vgmeta (const char *vg, size_t *size_r)
   fd = open (tmp, O_RDONLY|O_CLOEXEC);
   if (fd == -1) {
     reply_with_error ("%s", tmp);
+    unlink (tmp);
     return NULL;
   }
 
@@ -796,6 +798,7 @@ do_vgmeta (const char *vg, size_t *size_r)
         reply_with_error ("metadata is too large for message buffer");
         free (buf);
         close (fd);
+        unlink (tmp);
         return NULL;
       }
       buf2 = realloc (buf, alloc);
@@ -803,6 +806,7 @@ do_vgmeta (const char *vg, size_t *size_r)
         reply_with_perror ("realloc");
         free (buf);
         close (fd);
+        unlink (tmp);
         return NULL;
       }
       buf = buf2;
@@ -813,6 +817,7 @@ do_vgmeta (const char *vg, size_t *size_r)
       reply_with_perror ("read: %s", tmp);
       free (buf);
       close (fd);
+      unlink (tmp);
       return NULL;
     }
     if (rs == 0)
@@ -824,6 +829,7 @@ do_vgmeta (const char *vg, size_t *size_r)
   if (close (fd) == -1) {
     reply_with_perror ("close: %s", tmp);
     free (buf);
+    unlink (tmp);
     return NULL;
   }