Fail gracefully if no app executable is set

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ctrueden

src/main/java/org/scijava/desktop/DefaultDesktopService.java

@@ -288,6 +288,9 @@ private void maybeAutoInstallDesktopIntegrations() {
 			prefs.getBoolean(DesktopService.class, "installedOnce", false);
 		if (installedOnce) return;
 
+		// Without a launcher binary, there is nothing to register.
+		if (System.getProperty("scijava.app.executable") == null) return;
+
 		// We haven't installed the integration before now! So here we go.
 		// We use a dedicated thread to avoid blocking context creation completion;
 		// nothing in the desktop registration needs to be completed synchronously;

src/main/java/org/scijava/desktop/platform/linux/LinuxPlatform.java

@@ -202,10 +202,7 @@ public void syncDesktopIntegration(final boolean webLinks,
 
 		// An executable is required for any feature to work.
 		final String appExec = System.getProperty("scijava.app.executable");
-		if (appExec == null) {
-			throw new IOException(
-				"No executable path set (scijava.app.executable property)");
-		}
+		if (appExec == null) return;
 
 		final DesktopFile df = new DesktopFile(path);
 

src/main/java/org/scijava/desktop/platform/windows/WindowsPlatform.java

@@ -111,9 +111,7 @@ public void setWebLinksEnabled(final boolean enable) throws IOException {
 		final WindowsSchemeInstaller installer = new WindowsSchemeInstaller(log);
 		final String executablePath = System.getProperty("scijava.app.executable");
 
-		if (executablePath == null) {
-			throw new IOException("No executable path set (scijava.app.executable property)");
-		}
+		if (executablePath == null) return;
 
 		final Set<String> schemes = schemes();
 		for (final String scheme : schemes) {
@@ -183,9 +181,7 @@ public boolean isFileExtensionsToggleable() {
 	@Override
 	public void setFileExtensionsEnabled(final boolean enable) throws IOException {
 		final String executablePath = System.getProperty("scijava.app.executable");
-		if (executablePath == null) {
-			throw new IOException("No executable path set (scijava.app.executable property)");
-		}
+		if (executablePath == null) return;
 
 		final String executableName = getExecutableName();
 		if (executableName == null) {