backuptool: Add checks if it makes sense to execute commands

Change-Id: Ic83fc1168ac459b1bba5cef97d184ce2a9db4c68

prebuilt/common/bin/backuptool.sh

@@ -12,19 +12,27 @@ cp -f /tmp/install/bin/backuptool.functions /tmp
 
 # Preserve /system/addon.d in /tmp/addon.d
 preserve_addon_d() {
-  mkdir -p /tmp/addon.d/
-  cp -a /system/addon.d/* /tmp/addon.d/
-  chmod 755 /tmp/addon.d/*.sh
+  if [ -d /system/addon.d/ ]; then
+    mkdir -p /tmp/addon.d/
+    cp -a /system/addon.d/* /tmp/addon.d/
+    chmod 755 /tmp/addon.d/*.sh
+  fi
 }
 
-# Restore /system/addon.d in /tmp/addon.d
+# Restore /system/addon.d from /tmp/addon.d
 restore_addon_d() {
-  cp -a /tmp/addon.d/* /system/addon.d/
-  rm -rf /tmp/addon.d/
+  if [ -d /tmp/addon.d/ ]; then
+    cp -a /tmp/addon.d/* /system/addon.d/
+    rm -rf /tmp/addon.d/
+  fi
 }
 
 # Proceed only if /system is the expected major and minor version
 check_prereq() {
+# If there is no build.prop file the partition is probably empty.
+if [ ! -r /system/build.prop ]; then
+    return 0
+fi
 if ( ! grep -q "^ro.cm.version=$V.*" /system/build.prop ); then
   echo "Not backing up files from incompatible version: $V"
   return 0
@@ -63,9 +71,11 @@ check_whitelist() {
 
 # Execute /system/addon.d/*.sh scripts with $1 parameter
 run_stage() {
-for script in $(find /tmp/addon.d/ -name '*.sh' |sort -n); do
-  $script $1
-done
+if [ -d /tmp/addon.d/ ]; then
+  for script in $(find /tmp/addon.d/ -name '*.sh' |sort -n); do
+    $script $1
+  done
+fi
 }
 
 case "$1" in