Fixes the loading extensions under Linux

Author: emmanue1

app/src/main/groovy/org/jd/gui/service/extension/ExtensionService.groovy

@@ -13,7 +13,9 @@ class ExtensionService {
     protected ClassLoader extensionClassLoader = initClassLoader()
 
     protected ClassLoader initClassLoader() {
-        def extDirectory = new File("ext");
+        def jarUri = ExtensionService.class.protectionDomain.codeSource.location.toURI()
+        def baseDirectory = new File(jarUri).parent
+        def extDirectory = new File(baseDirectory, 'ext')
 
         if (extDirectory.exists() && extDirectory.isDirectory()) {
             List<URL> urls = []

build.gradle

@@ -172,8 +172,8 @@ ospackage {
     }
     from 'LICENSE', 'NOTICE', 'README.md'
 
-    postInstall 'cd /opt/'+ project.name+'; ln -s ./jd-gui-'+project.version+'.jar ./jd-gui.jar; xdg-icon-resource install --size 128 --novendor ./jd_icon_128.png jd-gui ; xdg-desktop-menu install ./*.desktop'
-    preUninstall 'cd /opt/'+ project.name+'; rm -f ./jd-gui.jar; xdg-desktop-menu uninstall ./*.desktop'
+    postInstall 'cd /opt/'+ project.name+'; ln -s ./jd-gui-'+project.version+'.jar ./jd-gui.jar; xdg-icon-resource install --size 128 --novendor ./jd_icon_128.png jd-gui; xdg-desktop-menu install ./*.desktop'
+    preUninstall 'cd /opt/'+ project.name+'; rm -f ./jd-gui.jar; rm -fr ./ext; xdg-desktop-menu uninstall ./*.desktop'
 }
 
 installOsxDist.dependsOn jar, copyAndReplaceVariablesInInfoPlist