patch 8.0.1671: crash when passing non-dict argument as env to job_start()

Problem:    Crash when passing non-dict argument as env to job_start().
Solution:   Check for valid argument. (Ozaki Kiichi, closes #2765)
diff --git a/src/version.c b/src/version.c
index 59ca7a8..8264bd9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -763,6 +763,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1671,
+/**/
     1670,
 /**/
     1669,