fix: incomplete escape in list at the end of file

Previously this resulted in invalid memory access.

Found by the fuzzer.

Author: flavorjones

src/yarp.c

@@ -6952,6 +6952,12 @@ parser_lex(yp_parser_t *parser) {
                 // literally. In this case we'll skip past the next character
                 // and find the next breakpoint.
                 if (*breakpoint == '\\') {
+                    // Check that we're not at the end of the file.
+                    if (breakpoint + 1 >= parser->end) {
+                        breakpoint = NULL;
+                        continue;
+                    }
+
                     yp_unescape_type_t unescape_type = lex_mode->as.list.interpolation ? YP_UNESCAPE_ALL : YP_UNESCAPE_MINIMAL;
                     size_t difference = yp_unescape_calculate_difference(parser, breakpoint, unescape_type, false);
 

test/yarp/fuzzer_test.rb

@@ -21,4 +21,5 @@ def snippet(name, source)
   snippet "incomplete binary number", "0b"
   snippet "incomplete octal number", "0o"
   snippet "incomplete hex number", "0x"
+  snippet "incomplete escaped list", "%w[\\"
 end