fix: don't OOM if file ends in a null byte not preceded by whitespace

Initially, I couldn't reproduce this because Neovim inserts a new line
at the end of the file. This prevents the `text` external rule to match
with 0 width, hence preventing the OOM.

Since at the start of `scan_text` we call `lexer->mark_end`, advancing
the state of the lexer inside the while loop doesn't increase the size
of the identified token until the next iteration. Before this commit,
when the last character of a file wasn't whitespace, the `text` rule
matched with 0 width, producing the OOM. Making the loop a `while
(true)` and checking at the end of it for `lexer->eof(lexer)` solves
this problem.

src/scanner.c

@@ -377,7 +377,7 @@ static bool scan_text(Scanner *scanner, TSLexer *lexer) {
                               : scanner->end_delimiter.size;
   int start_i = 0;
   int end_i = 0;
-  while (!lexer->eof(lexer)) {
+  while (true) {
     int ith_start = get_delimiter(scanner->start_delimiter, start_i,
                                   DEFAULT_START_DELIMITER);
     if (lexer->lookahead == ith_start) {
@@ -389,9 +389,8 @@ static bool scan_text(Scanner *scanner, TSLexer *lexer) {
       }
       start_i = 0;
     }
-    if (start_i == start_delimiter_max) {
+    if (start_i == start_delimiter_max)
       break;
-    }
 
     int ith_end =
         get_delimiter(scanner->end_delimiter, end_i, DEFAULT_END_DELIMITER);
@@ -404,9 +403,11 @@ static bool scan_text(Scanner *scanner, TSLexer *lexer) {
       }
       end_i = 0;
     }
-    if (end_i == end_delimiter_max) {
+    if (end_i == end_delimiter_max)
+      break;
+
+    if (lexer->eof(lexer))
       break;
-    }
 
     lexer->advance(lexer, false);
   }