reset instruction pointers with calls, make HCPrinter::range_from safe (#1233)

src/heap_print.rs

@@ -376,7 +376,7 @@ impl HCValueOutputter for PrinterOutputter {
     }
 
     fn range_from(&self, index: RangeFrom<usize>) -> &str {
-        &self.contents.as_str()[index]
+        &self.contents.as_str().get(index).unwrap_or("")
     }
 }