input: ingest as verbatim just one control code or one or two escapes

Leave the rest of any escape sequence to be processed normally, which
should be possible because those characters are all in ASCII range.

This fixes https://savannah.gnu.org/bugs/?48318.

src/proto.h

@@ -776,7 +776,7 @@ long get_unicode_kbinput(WINDOW *win, int kbinput);
 int get_control_kbinput(int kbinput);
 void unparse_kbinput(char *output, size_t output_len);
 int *get_verbatim_kbinput(WINDOW *win, size_t *kbinput_len);
-int *parse_verbatim_kbinput(WINDOW *win, size_t *kbinput_len);
+int *parse_verbatim_kbinput(WINDOW *win, size_t *count);
 #ifndef DISABLE_MOUSE
 int get_mouseinput(int *mouse_x, int *mouse_y, bool allow_shortcuts);
 #endif

src/winio.c

@@ -1311,13 +1311,13 @@ int *get_verbatim_kbinput(WINDOW *win, size_t *kbinput_len)
     return retval;
 }
 
-/* Read in a stream of all available characters, and return the length
- * of the string in kbinput_len.  Translate the first few characters of
- * the input into the corresponding multibyte value if possible.  After
- * that, leave the input as-is. */
-int *parse_verbatim_kbinput(WINDOW *win, size_t *kbinput_len)
+/* Read in one control character (or an iTerm double Escape), or convert a
+ * series of six digits into a Unicode codepoint.  Return in count either 1
+ * (for a control character or the first byte of a multibyte sequence), or 2
+ * (for an iTerm double Escape). */
+int *parse_verbatim_kbinput(WINDOW *win, size_t *count)
 {
-    int *kbinput, *retval;
+    int *kbinput;
 
     /* Read in the first code. */
     while ((kbinput = get_input(win, 1)) == NULL)
@@ -1326,8 +1326,8 @@ int *parse_verbatim_kbinput(WINDOW *win, size_t *kbinput_len)
 #ifndef NANO_TINY
     /* When the window was resized, abort and return nothing. */
     if (*kbinput == KEY_WINCH) {
-	*kbinput_len = 0;
 	free(kbinput);
+	*count = 0;
 	return NULL;
     }
 #endif
@@ -1369,18 +1369,19 @@ int *parse_verbatim_kbinput(WINDOW *win, size_t *kbinput_len)
 	}
     } else
 #endif /* ENABLE_UTF8 */
-
 	/* Put back the first code. */
 	unget_input(kbinput, 1);
 
     free(kbinput);
 
-    /* Get the complete sequence, and save the characters in it as the
-     * result. */
-    *kbinput_len = key_buffer_len;
-    retval = get_input(NULL, *kbinput_len);
+    *count = 1;
 
-    return retval;
+    /* If this is an iTerm double escape, take both Escapes. */
+    if (key_buffer_len > 3 && *key_buffer == ESC_CODE &&
+		key_buffer[1] == ESC_CODE && key_buffer[2] == '[')
+	*count = 2;
+
+    return get_input(NULL, *count);
 }
 
 #ifndef DISABLE_MOUSE