Term fill in String#{,l,r}strip! even when SHARABLE_MIDDLE_SUBSTRING

Each of these methods calls str_modify_keep_cr before
term filling, which should ensure the backing string
uses private memory, and therefore term filling should
not affect other strings.

Skipping the term filling was added in
a707ab4.

Fixes [Bug #12540]

string.c

@@ -9322,9 +9322,7 @@ rb_str_lstrip_bang(VALUE str)
 	s = start + loffset;
 	memmove(start, s, len);
 	STR_SET_LEN(str, len);
-#if !SHARABLE_MIDDLE_SUBSTRING
 	TERM_FILL(start+len, rb_enc_mbminlen(enc));
-#endif
 	return str;
     }
     return Qnil;
@@ -9411,9 +9409,7 @@ rb_str_rstrip_bang(VALUE str)
 	long len = olen - roffset;
 
 	STR_SET_LEN(str, len);
-#if !SHARABLE_MIDDLE_SUBSTRING
 	TERM_FILL(start+len, rb_enc_mbminlen(enc));
-#endif
 	return str;
     }
     return Qnil;
@@ -9482,9 +9478,7 @@ rb_str_strip_bang(VALUE str)
 	    memmove(start, start + loffset, len);
 	}
 	STR_SET_LEN(str, len);
-#if !SHARABLE_MIDDLE_SUBSTRING
 	TERM_FILL(start+len, rb_enc_mbminlen(enc));
-#endif
 	return str;
     }
     return Qnil;