Add test if import and migrate script exist

Author: ioppermann

run.sh

@@ -3,20 +3,24 @@
 # First run the import program. It will read the db.dir from the config file in order to
 # find an old v1.json. This will be converted to the new db format.
 
-./bin/import
-if [ $? -ne 0 ]; then
-    exit 1
+if [ -x ./bin/import ]; then
+    ./bin/import
+    if [ $? -ne 0 ]; then
+        exit 1
+    fi
 fi
 
 # Run the FFmpeg migration program. In case a FFmpeg 5 binary is present, it will create a
 # backup of the current DB and modify the FFmpeg parameter such that they are compatible
 # with FFmpeg 5.
 
-./bin/ffmigrate
-if [ $? -ne 0 ]; then
-    exit 1
+if [ -x ./bin/ffmigrate ]; then
+    ./bin/ffmigrate
+    if [ $? -ne 0 ]; then
+        exit 1
+    fi
 fi
 
 # Now run the core with the possibly converted configuration.
 
-./bin/core
+exec ./bin/core