[wasm][asm.js] Fix incorrect stack depth in some returns.

Previously we allowed unreachable returns to be skipped.
This won't work if we strictly follow the spec.

BUG=None
TEST=Manual against more strict wasm validation
R=titzer@chromium.org,rossberg@chromium.org

Review-Url: https://codereview.chromium.org/2668873003
Cr-Commit-Position: refs/heads/master@{#42833}

src/asmjs/asm-wasm-builder.cc

@@ -216,7 +216,6 @@ class AsmWasmBuilderImpl final : public AstVisitor<AsmWasmBuilderImpl> {
       }
       RECURSE(Visit(stmt));
       if (typer_failed_) break;
-      if (stmt->IsJump()) break;
     }
   }