[ddc] Avoid crash when compiling super initializer

We can't find a reproduction but for now it seems better to
avoid crashing and just keep compiling without adding any
source information.

Issue: dart-lang/sdk#50465
Fixes: dart-lang/sdk#50394
Change-Id: I9bba60c35647ec1cb5894d0be20a97228098880a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/269741
Commit-Queue: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Mark Zhou <markzipan@google.com>

Author: nshahan

pkg/dev_compiler/lib/src/kernel/compiler.dart

@@ -1731,7 +1731,10 @@ class ProgramCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
     var superCall = node.initializers.whereType<SuperInitializer>().firstOrNull;
     var jsSuper = _emitSuperConstructorCallIfNeeded(cls, className, superCall);
     if (jsSuper != null) {
-      body.add(jsSuper..sourceInformation = _nodeStart(superCall!));
+      // TODO(50465) Fix incorrect assumption there should always be a super
+      // initializer here.
+      if (superCall != null) jsSuper.sourceInformation = _nodeStart(superCall);
+      body.add(jsSuper);
     }
 
     body.add(_emitFunctionScopedBody(fn));