fix: lexer out of bounds

example.rx

@@ -1,3 +1,18 @@
+extern putchar
+
+fn hello() {
+    local h = 72
+    putchar(h)
+    local e = h - 3
+    putchar(e)
+    local l = h + 4
+    putchar(l)
+    putchar(l)
+    local o = 100 - 21
+    putchar(o)
+}
+
 fn main() {
+    hello()
     putchar(3 * 3 + 1)
 }