Make downloading the version json not print the big cache miss message

Author: LexManos

src/main/java/net/minecraftforge/mcmaven/cli/MCPTask.java

@@ -269,7 +269,7 @@ private static void writeFiles(MCPTaskFactory mcpTaskFactory, File output) {
         try {
             return mcpTaskFactory.findStep(step).execute().getAbsolutePath();
         } catch (Exception e) {
-            LOGGER.error("Cannot serialize output path for MCP step: " + step);
+            LOGGER.error("Cannot serialize output path for MCP step: " + step, e);
             return null;
         }
     }

src/main/java/net/minecraftforge/mcmaven/impl/repo/mcpconfig/MinecraftTasks.java

@@ -93,7 +93,15 @@ private File downloadVersionJson() {
         if (target.exists() && cache.isSame())
             return target;
 
-        Mavenizer.assertNotCacheOnly();
+        // The manifest doesn't contain anything we can key off off, so this happens often
+        // Do don't do the big warn if we get here.
+        if (Mavenizer.isCacheOnly())
+            Mavenizer.assertNotCacheOnly();
+
+        // If we are offline, but the file exists, use it
+        if (Mavenizer.isOffline() && target.exists())
+            return target;
+
         Mavenizer.assertOnline();
 
         var manifest = JsonData.launcherManifest(manifestF);