func_curl: Don't trim response text on non-ASCII characters

The characters 0x80-0xFF were trimmed as well as 0x00-0x20 because of
a signed comparison.

ASTERISK-25669 #close
Reported by: Jesper
patches:
  strings.curl.trim.patch submitted by Jesper (License 5518)

Change-Id: Ia51e169f24e3252a7ebbaab3728630138ec6f60a

include/asterisk/strings.h

@@ -688,7 +688,7 @@ void ast_str_trim_blanks(struct ast_str *buf),
 	if (!buf) {
 		return;
 	}
-	while (buf->__AST_STR_USED && buf->__AST_STR_STR[buf->__AST_STR_USED - 1] < 33) {
+	while (buf->__AST_STR_USED && ((unsigned char) buf->__AST_STR_STR[buf->__AST_STR_USED - 1]) < 33) {
 		buf->__AST_STR_STR[--(buf->__AST_STR_USED)] = '\0';
 	}
 }