[gnome-usage] swap-speedometer: Initialize label to "0%"

[Felipe Borges <felipeborges src gnome org>]

commit c4119bdb1c151e22cd94661390f138f505fc8550
Author: Felipe Borges <felipeborges gnome org>
Date:   Tue Jan 2 11:24:44 2018 +0100

    swap-speedometer: Initialize label to "0%"
    
    This way we show the correct information when there's no swap
    partition available.
    
    Fixes #27

 src/swap-speedometer.vala | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)
---
diff --git a/src/swap-speedometer.vala b/src/swap-speedometer.vala
index 85670ca..e194d65 100644
--- a/src/swap-speedometer.vala
+++ b/src/swap-speedometer.vala
@@ -42,13 +42,14 @@ namespace Usage
         construct {
             var monitor = SystemMonitor.get_default();
             Timeout.add_seconds(1, () => {
-                var percentage = (((double) monitor.swap_usage / monitor.swap_total) * 100);
+                var available = (monitor.swap_total - monitor.swap_usage);
+                var percentage = 0.0;
+                if (available > 0)
+                    percentage = (((double) monitor.swap_usage / monitor.swap_total) * 100);
 
                 this.speedometer.percentage = (int)percentage;
                 label.label = "%d".printf((int)percentage) + "%";
 
-                var available = (monitor.swap_total - monitor.swap_usage);
-
                 swap_used.label = Utils.format_size_values(monitor.swap_usage);
                 swap_available.label = Utils.format_size_values(available);