Fixed off-by-one spans in MIR borrowck errors.

Author: davidtwco

src/librustc_mir/build/scope.rs

@@ -695,10 +695,17 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 if let DropKind::Value { .. } = drop_kind {
                     scope.needs_cleanup = true;
                 }
+
                 let region_scope_span = region_scope.span(self.hir.tcx(),
                                                           &self.hir.region_scope_tree);
-                // Attribute scope exit drops to scope's closing brace
-                let scope_end = region_scope_span.with_lo(region_scope_span.hi());
+                // Attribute scope exit drops to scope's closing brace.
+                // Without this check when finding the endpoint, we'll run into an ICE.
+                let scope_end = if region_scope_span.hi().0 == 0 {
+                    region_scope_span
+                } else {
+                    region_scope_span.end_point()
+                };
+
                 scope.drops.push(DropData {
                     span: scope_end,
                     location: place.clone(),