treesitter: check for integer overflow (#12135)

Sometimes treesitter calls for an invalid column within a line, checking
that the column is actually valid and forcing the value avoids an
integer overflow and an infinite sequence of invalid reads.

Fixes #12131

src/nvim/lua/treesitter.c

@@ -271,6 +271,10 @@ static const char *input_cb(void *payload, uint32_t byte_index,
   }
   char_u *line = ml_get_buf(bp, position.row+1, false);
   size_t len = STRLEN(line);
+
+  if (position.column > len) {
+    *bytes_read = 0;
+  } else {
     size_t tocopy = MIN(len-position.column, BUFSIZE);
 
     memcpy(buf, line+position.column, tocopy);
@@ -283,6 +287,7 @@ static const char *input_cb(void *payload, uint32_t byte_index,
       buf[tocopy] = '\n';
       (*bytes_read)++;
     }
+  }
   return buf;
 #undef BUFSIZE
 }