Deal with save corruption correctly

src/vnmodal.ts

@@ -169,9 +169,6 @@ class SaveGameCathexis {
     this.#drawpile = new DrawPile();
     this.#file = file;
     this.#error = error;
-    if (this.#error != null && this.#file != null) {
-      throw new Error("can't have a savefile _and_ an error");
-    }
     this.#done = false;
   }
 
@@ -186,8 +183,12 @@ class SaveGameCathexis {
     this.#drawpile.clear();
     this.#drawpile.add(0, () => {
       D.drawText(
-        this.#error
-          ? `Your save file was invalid and could not be loaded:
+        this.#error && this.#file
+          ? `A save was invalid. Continue from an alternate save?
+
+${this.#error}`
+          : this.#error
+            ? `Your save was invalid:
 
 ${this.#error}`
           : "Resume from save?",