patch 8.2.3589: failure when "term_rows" of term_start() is an unusual value

Problem:    Failure when the "term_rows" argument of term_start() is an
            unusual value.
Solution:   Limit to range of zero to 1000. (closes #9116)
diff --git a/runtime/doc/terminal.txt b/runtime/doc/terminal.txt
index 510f1c3..47b04df 100644
--- a/runtime/doc/terminal.txt
+++ b/runtime/doc/terminal.txt
@@ -871,7 +871,8 @@
 		   "term_name"	     name to use for the buffer name, instead
 				     of the command name.
 		   "term_rows"	     vertical size to use for the terminal,
-				     instead of using 'termwinsize'
+				     instead of using 'termwinsize'; valid
+				     range is from zero to 1000
 		   "term_cols"	     horizontal size to use for the terminal,
 				     instead of using 'termwinsize'
 		   "vertical"	     split the window vertically; note that