fix: comment followed by whitespace at end of file

Previously this resulted in invalid memory access.

Found by the fuzzer.

Author: flavorjones

src/yarp.c

@@ -5921,7 +5921,7 @@ parser_lex(yp_parser_t *parser) {
 
                                 // If this is not followed by a comment, then we can break out
                                 // of this loop.
-                                if (*following != '#') break;
+                                if (peek_at(parser, following) != '#') break;
 
                                 // If there is a comment, then we need to find the end of the
                                 // comment and continue searching from there.

test/yarp/fuzzer_test.rb

@@ -16,6 +16,7 @@ def snippet(name, source)
   snippet "incomplete symbol", ":"
   snippet "incomplete escaped string", '"\\'
   snippet "trailing comment", "1\n#\n"
+  snippet "comment followed by whitespace at end of file", "1\n#\n "
   snippet "trailing asterisk", "a *"
   snippet "incomplete decimal number", "0d"
   snippet "incomplete binary number", "0b"