Make stack frames without columns print correctly.

pkg/stack_trace/lib/src/frame.dart

Index: pkg/stack_trace/lib/src/frame.dart
diff --git a/pkg/stack_trace/lib/src/frame.dart b/pkg/stack_trace/lib/src/frame.dart
index 797bef173ba1a6623bb1942ca3b4ad6a3c0076cf..383a156f9c11d011aa328bda02d7dbd3ceaca969 100644
--- a/pkg/stack_trace/lib/src/frame.dart
+++ b/pkg/stack_trace/lib/src/frame.dart
@@ -78,7 +78,8 @@ class Frame {
 
   /// A human-friendly description of the code location.
   String get location {
-    if (line == null || column == null) return library;
+    if (line == null) return library;
+    if (column == null) return '$library $line';
     return '$library $line:$column';
   }