[chronojump] ForceSensor: fix on opened signal being deleted from SO

[Xavier de Blas <xaviblas src gnome org>]

commit ee04527fc823c64a56beb61fbd9451ddf3ff55d6
Author: Xavier de Blas <xaviblas gmail com>
Date:   Mon May 27 00:09:37 2019 -0300

    ForceSensor: fix on opened signal being deleted from SO

 src/forceSensor.cs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/src/forceSensor.cs b/src/forceSensor.cs
index 65d5c5fd..a26f64b8 100644
--- a/src/forceSensor.cs
+++ b/src/forceSensor.cs
@@ -667,13 +667,15 @@ public class ForceSensorAnalyzeInstant
        {
                fscAIPoints = new ForceSensorCapturePoints(graphWidth, graphHeight);
 
-//TODO: check file exists...
                List<string> contents = Util.ReadFileAsStringList(file);
                bool headersRow = true;
 
                //initialize
                forceSensorValues = new ForceSensorValues();
 
+               if(contents == null)
+                       return;
+
                foreach(string str in contents)
                {
                        if(headersRow)