patch 8.2.0370: the typebuf_was_filled flag is sometimes not reset

Problem:    The typebuf_was_filled flag is sometimes not reset, which may
            cause a hang.
Solution:   Make sure typebuf_was_filled is reset when the typeahead buffer is
            empty.
diff --git a/src/getchar.c b/src/getchar.c
index 7df4bce..6b1068d 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -421,6 +421,10 @@
 	// remove mapped characters at the start only
 	typebuf.tb_off += typebuf.tb_maplen;
 	typebuf.tb_len -= typebuf.tb_maplen;
+#if defined(FEAT_CLIENTSERVER) || defined(FEAT_EVAL)
+	if (typebuf.tb_len == 0)
+	    typebuf_was_filled = FALSE;
+#endif
     }
     else
     {
@@ -1283,6 +1287,9 @@
     typebuf.tb_no_abbr_cnt = 0;
     if (++typebuf.tb_change_cnt == 0)
 	typebuf.tb_change_cnt = 1;
+#if defined(FEAT_CLIENTSERVER) || defined(FEAT_EVAL)
+    typebuf_was_filled = FALSE;
+#endif
     return OK;
 }