Handle ENOMEM during fork()

Reported-by: syzbot+638411bd4594d01e2d70@syzkaller.appspotmail.com

Signed-off-by: Barret Rhoden <brho@cs.berkeley.edu>

kern/src/syscall.c

diff --git a/kern/src/syscall.c b/kern/src/syscall.c
index 43164ec..efda04f 100644
--- a/kern/src/syscall.c
+++ b/kern/src/syscall.c
@@ -895,8 +895,10 @@
 	env_t* env;
 
 	ret = proc_alloc(&env, current, PROC_DUP_FGRP);
-	assert(!ret);
-	assert(env != NULL);
+	if (ret < 0) {
+		set_errno(-ret);
+		return -1;
+	}
 	proc_set_progname(env, e->progname);
 
 	/* Can't really fork if we don't have a current_ctx to fork */