Fix another PAL unit test

Pal/src/db_main.c

@@ -371,8 +371,13 @@ has_manifest:
             exec_uri[exec_strlen] = '\0';
             ret = _DkStreamOpen(&exec_handle, exec_uri, PAL_ACCESS_RDONLY,
                                 0, 0, 0);
-            if (ret < 0)
-                init_fail(-ret, "cannot open executable");
+            // DEP 3/20/17: There are cases where we want to let
+            // the PAL start up without a main executable.  Don't
+            // die here, just free the exec_uri buffer.
+            if (ret < 0) {
+                free(exec_uri);
+                exec_uri = NULL;
+            }
         }
     }