patch 8.0.0746: when :term fails the job is not properly cleaned up

Problem:    When :term fails the job is not properly cleaned up.
Solution:   Free the terminal. Handle a job that failed to start. (closes
            #1858)

src/channel.c

@@ -5189,6 +5189,11 @@ job_stop(job_T *job, typval_T *argvars, char *type)
 	    return 0;
 	}
     }
+    if (job->jv_status == JOB_FAILED)
+    {
+	ch_log(job->jv_channel, "Job failed to start, job_stop() skipped");
+	return 0;
+    }
     if (job->jv_status == JOB_ENDED)
     {
 	ch_log(job->jv_channel, "Job has already ended, job_stop() skipped");

src/os_unix.c

@@ -5475,6 +5475,8 @@ mch_stop_job(job_T *job, char_u *how)
 	job_pid = -job_pid;
 #endif
 
+    /* Never kill ourselves! */
+    if (job_pid != 0)
 	kill(job_pid, sig);
 
     return OK;

src/terminal.c

@@ -203,6 +203,9 @@ ex_terminal(exarg_T *eap)
     }
     else
     {
+	free_terminal(term);
+	curbuf->b_term = NULL;
+
 	/* Wiping out the buffer will also close the window and call
 	 * free_terminal(). */
 	do_buffer(DOBUF_WIPE, DOBUF_CURRENT, FORWARD, 0, TRUE);
@@ -235,7 +238,8 @@ free_terminal(term_T *term)
 
     if (term->tl_job != NULL)
     {
-	if (term->tl_job->jv_status != JOB_ENDED)
+	if (term->tl_job->jv_status != JOB_ENDED
+				      && term->tl_job->jv_status != JOB_FAILED)
 	    job_stop(term->tl_job, NULL, "kill");
 	job_unref(term->tl_job);
     }
@@ -941,7 +945,9 @@ term_and_job_init(term_T *term, int rows, int cols, char_u *cmd)
     setup_job_options(&opt, rows, cols);
     term->tl_job = job_start(argvars, &opt);
 
-    return term->tl_job != NULL ? OK : FAIL;
+    return term->tl_job != NULL
+	&& term->tl_job->jv_channel != NULL
+	&& term->tl_job->jv_status != JOB_FAILED ? OK : FAIL;
 }
 
 /*

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    746,
 /**/
     745,
 /**/