smartctlUtil: do not reference error when not failing, do not return empty data if none (#221)

The `smartctl -j --scan` command may not fail and list drives properly
while `smartctl -j --info /dev/sda` may fail because of missing
permissions.

This error was making the extension on fail entirely when smartctl
was selected as a disk temperature sensor provider while the
user does not have enogh permission to do so.

Also makes sure smartctl can be properly called if path contains
a whitespace.

freon@UshakovVasilii_Github.yahoo.com/smartctlUtil.js

@@ -4,7 +4,7 @@ const Me = imports.misc.extensionUtils.getCurrentExtension();
 const ByteArray = imports.byteArray;
 function getSmartData (argv){
     const smartctl = GLib.find_program_in_path('smartctl')
-    return JSON.parse(ByteArray.toString( GLib.spawn_command_line_sync(`${smartctl} ${argv} -j`)[1] ))
+    return JSON.parse(ByteArray.toString( GLib.spawn_command_line_sync(`'${smartctl}' ${argv} -j`)[1] ))
 }
 
 var smartctlUtil  = class {
@@ -12,10 +12,9 @@ var smartctlUtil  = class {
         this._smartDevices = [];
         try {
             this._smartDevices = getSmartData("--scan")["devices"]
-	    global.log('[FREON] test devices: ' + e);
         } catch (e) {
             global.log('[FREON] Unable to find smart devices: ' + e);
-        }        
+        }
         this._updated = true;
     }
 
@@ -33,11 +32,19 @@ var smartctlUtil  = class {
 
     get temp() {
         return this._smartDevices.map(device => {
+            const info = getSmartData(`--info ${device["name"]}`);
+            if (info["smartctl"]["exit_status"] != 0)
+                return null;
+
+            const attributes = getSmartData(`--attributes ${device["name"]}`);
+            if (attributes["smartctl"]["exit_status"] != 0)
+                return null;
+
             return {
-                label: getSmartData(`--info ${device["name"]}`)["model_name"],
-                temp: parseFloat(getSmartData(`--attributes ${device["name"]}`).temperature.current)
+                label: info["model_name"],
+                temp: parseFloat(attributes.temperature.current)
             }
-        })
+        }).filter(entry => entry != null);
     }
 
     destroy(callback) {