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)

src/version.c

@@ -762,6 +762,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1671,
 /**/
     1670,
 /**/