Check that cpu temperature can be detected

src/freedombone-installer

@@ -1504,9 +1504,11 @@ function update_system_monitor {
         used_memory_percent=$((used_memory * 100 / total_memory))
 
         cpu_temperature=0
-        cpu_temp=$(cat /sys/class/thermal/thermal_zone*/temp | head -n 1)
-        if [ "$cpu_temp" ]; then
-            cpu_temperature=$((cpu_temp / 1000))
+        if [ -f /sys/class/thermal/thermal_zone0/temp ]; then
+            cpu_temp=$(cat /sys/class/thermal/thermal_zone*/temp | head -n 1)
+            if [ "$cpu_temp" ]; then
+                cpu_temperature=$((cpu_temp / 1000))
+            fi
         fi
 
         test_drive=/dev/sda1

src/freedombone-utils-webadmin

@@ -753,9 +753,11 @@ function webadmin_update_system_monitor {
     used_memory_percent=$((used_memory * 100 / total_memory))
 
     cpu_temperature=0
-    cpu_temp=$(cat /sys/class/thermal/thermal_zone*/temp | head -n 1)
-    if [ "$cpu_temp" ]; then
-        cpu_temperature=$((cpu_temp / 1000))
+    if [ -f /sys/class/thermal/thermal_zone0/temp ]; then
+        cpu_temp=$(cat /sys/class/thermal/thermal_zone*/temp | head -n 1)
+        if [ "$cpu_temp" ]; then
+            cpu_temperature=$((cpu_temp / 1000))
+        fi
     fi
 
     test_drive=/dev/sda1