patch 8.0.0816: crash when using invalid buffer number

Problem:    Crash when using invalid buffer number.
Solution:   Check for NULL buffer. (Yasuhiro Matsumoto, closes #1899)

src/terminal.c

@@ -1686,7 +1686,7 @@ term_get_buf(typval_T *argvars)
     ++emsg_off;
     buf = get_buf_tv(&argvars[0], FALSE);
     --emsg_off;
-    if (buf->b_term == NULL)
+    if (buf == NULL || buf->b_term == NULL)
 	return NULL;
     return buf;
 }

src/testdir/test_terminal.vim

@@ -54,6 +54,9 @@ func Test_terminal_scrape()
   call assert_equal(1, len(termlist))
   call assert_equal(buf, termlist[0])
 
+  " Nothing happens with invalid buffer number
+  call term_wait(1234)
+
   call term_wait(buf)
   call Check_123(buf)
 
@@ -64,4 +67,5 @@ func Test_terminal_scrape()
   call Check_123(buf)
 
   exe buf . 'bwipe'
+  call delete('Xtext')
 endfunc

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    816,
 /**/
     815,
 /**/