fix: add empty string checks for VM detection and battery verification

Author: draphy

install.sh

@@ -2852,6 +2852,13 @@ configure_battery_limit() {
     local verify_value
     verify_value=$(cat "$battery_path" 2>/dev/null | head -1)
 
+    # Skip verification if we couldn't read the value
+    if [ -z "$verify_value" ]; then
+        print_warning "Could not verify battery limit (unable to read value)"
+        FAILED_ITEMS+=("battery-limit-read")
+        return 0
+    fi
+
     # Type-specific verification
     case "$battery_type" in
         huawei)
@@ -3137,7 +3144,8 @@ configure_vm() {
     if command -v systemd-detect-virt &>/dev/null; then
         local virt_type
         virt_type=$(systemd-detect-virt 2>/dev/null || echo "none")
-        if [ "$virt_type" != "none" ]; then
+        # Only detect VM if virt_type is non-empty and not "none"
+        if [ -n "$virt_type" ] && [ "$virt_type" != "none" ]; then
             is_vm=true
             print_step "VM detected: $virt_type"
         fi