stats: Check for errors from copyout()

This is in preparation for annotating copyin() and related functions
with __result_use_check.

MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D43179

sys/kern/subr_stats.c

@@ -1107,13 +1107,19 @@ stats_v1_blob_clone(struct statsblobv1 **dst, size_t dstmaxsz,
 		 */
 #ifdef _KERNEL
 		if (flags & SB_CLONE_USRDSTNOFAULT)
-			copyout_nofault(src, *dst,
+			error = copyout_nofault(src, *dst,
 			    offsetof(struct statsblob, maxsz));
 		else if (flags & SB_CLONE_USRDST)
-			copyout(src, *dst, offsetof(struct statsblob, maxsz));
+			error = copyout(src, *dst,
+			    offsetof(struct statsblob, maxsz));
 		else
 #endif
 			memcpy(*dst, src, offsetof(struct statsblob, maxsz));
+#ifdef _KERNEL
+		if (error != 0)
+			goto out;
+#endif
+
 
 		if (dstmaxsz >= src->cursz) {
 			postcurszlen = src->cursz -
@@ -1125,14 +1131,18 @@ stats_v1_blob_clone(struct statsblobv1 **dst, size_t dstmaxsz,
 		}
 #ifdef _KERNEL
 		if (flags & SB_CLONE_USRDSTNOFAULT)
-			copyout_nofault(&(src->cursz), &((*dst)->cursz),
+			error = copyout_nofault(&(src->cursz), &((*dst)->cursz),
 			    postcurszlen);
 		else if (flags & SB_CLONE_USRDST)
-			copyout(&(src->cursz), &((*dst)->cursz), postcurszlen);
+			error = copyout(&(src->cursz), &((*dst)->cursz),
+			    postcurszlen);
 		else
 #endif
 			memcpy(&((*dst)->cursz), &(src->cursz), postcurszlen);
 	}
+#ifdef _KERNEL
+out:
+#endif
 
 	return (error);
 }