fix(compiler-cli): avoid producing source mappings for host views (#19965)

The host view doesn't map back to user code so the template compiler
produces a blank `url` for them.

PR Close #19965

packages/compiler-cli/src/transformers/node_emitter.ts

@@ -144,6 +144,7 @@ class _NodeEmitterVisitor implements StatementVisitor, ExpressionVisitor {
       const span = node.sourceSpan;
       if (span.start.file == span.end.file) {
         const file = span.start.file;
+        if (file.url) {
           let source = this._templateSources.get(file);
           if (!source) {
             source = ts.createSourceMapSource(file.url, file.content, pos => pos);
@@ -152,6 +153,7 @@ class _NodeEmitterVisitor implements StatementVisitor, ExpressionVisitor {
           return {pos: span.start.offset, end: span.end.offset, source};
         }
       }
+    }
     return null;
   }