Fix overflow of string reverse iteration

ChJR · ChJR · commit 3e3bd07ff8aa · 2020-11-20T02:46:53.000+09:00
This issue does not appear in CI.
diff --git a/vm/src/builtins/pystr.rs b/vm/src/builtins/pystr.rs
@@ -180,7 +180,11 @@ impl PyIter for PyStrReverseIterator {
                     break;
                 }
             }
-            start.unwrap_or(end - 4)
+            if end < 4 {
+                start.unwrap_or(0)
+            } else {
+                start.unwrap_or(end - 4)
+            }
         };
 
         let stored = zelf.position.swap(start);

Original file line number	Diff line number	Diff line change
`@@ -180,7 +180,11 @@ impl PyIter for PyStrReverseIterator {`
`180`	`180`	`break;`
`181`	`181`	`}`
`182`	`182`	`}`
`183`		`- start.unwrap_or(end - 4)`
	`183`	`+ if end < 4 {`
	`184`	`+ start.unwrap_or(0)`
	`185`	`+ } else {`
	`186`	`+ start.unwrap_or(end - 4)`
	`187`	`+ }`
`184`	`188`	`};`
`185`	`189`
`186`	`190`	`let stored = zelf.position.swap(start);`