merge revision(s) ade56737e2273847426214035c0ff2340b43799a: [Backport #20190]

	Fix coderange of invalid_encoding_string.<<(ord)

	Appending valid encoding character can change coderange from invalid to valid.
	Example: "\x95".force_encoding('sjis')<<0x5C will be a valid string "\x{955C}"
	---
	 string.c                 | 6 +++++-
	 test/ruby/test_string.rb | 3 +++
	 2 files changed, 8 insertions(+), 1 deletion(-)

1 files changed, 5 insertions, 1 deletions

diff --git a/string.c b/string.c
index 923460a8f5..1f7321a1ce 100644
--- a/string.c
+++ b/string.c
@@ -3502,8 +3502,12 @@ rb_str_concat(VALUE str1, VALUE str2)
         }
         rb_str_resize(str1, pos+len);
         memcpy(RSTRING_PTR(str1) + pos, buf, len);
-        if (cr == ENC_CODERANGE_7BIT && code > 127)
+        if (cr == ENC_CODERANGE_7BIT && code > 127) {
             cr = ENC_CODERANGE_VALID;
+        }
+        else if (cr == ENC_CODERANGE_BROKEN) {
+            cr = ENC_CODERANGE_UNKNOWN;
+        }
         ENC_CODERANGE_SET(str1, cr);
     }
     return str1;