incusd/instance/common: Check PID validity

For pid = -1 skip Stat file not found error.

Signed-off-by: JUN JIE NAN <[email protected]>

Author: nanjj

internal/server/instance/drivers/driver_common.go

@@ -1597,6 +1597,10 @@ func (d *common) balanceNUMANodes() error {
 
 // Gets the process starting time.
 func (d *common) processStartedAt(pid int) (time.Time, error) {
+	if pid < 1 {
+		return time.Time{}, fmt.Errorf("Invalid PID %q", pid)
+	}
+
 	file, err := os.Stat(fmt.Sprintf("/proc/%d", pid))
 	if err != nil {
 		return time.Time{}, err