Fix crash when system has no swap

src/system.js

@@ -70,9 +70,11 @@ async function hdparm(file) {
 async function getSwaps() {
     const [error, stdout] = await safe(shell.exec('getSwaps', 'swapon --noheadings --raw --bytes --show=type,size,used,name', {}));
     if (error) return {};
+    const output = stdout.trim();
+    if (!output) return {}; // no swaps
 
     const swaps = {};
-    for (const line of stdout.trim().split('\n')) {
+    for (const line of output.split('\n')) {
         const parts = line.split(' ', 4);
         const name = parts[3];
         swaps[name] = {