EA-66942 diff: do not create OpenFileDescriptor with default project

a better solution would be to use 'null' project everywhere, using Default only when applicable and necessary. But this is not possible without removing/fixing of old DiffPanelImpl / DirDiff*.

platform/diff-impl/src/com/intellij/diff/contents/BinaryFileContentImpl.java

@@ -42,7 +42,7 @@ public class BinaryFileContentImpl implements DiffContent, BinaryFileContent {
   @Nullable
   @Override
   public OpenFileDescriptor getOpenFileDescriptor() {
-    if (myProject == null) return null;
+    if (myProject == null || myProject.isDefault()) return null;
     return new OpenFileDescriptor(myProject, myFile);
   }
 

platform/diff-impl/src/com/intellij/diff/contents/DirectoryContentImpl.java

@@ -35,7 +35,7 @@ public class DirectoryContentImpl implements DiffContent, DirectoryContent {
   @Nullable
   @Override
   public OpenFileDescriptor getOpenFileDescriptor() {
-    if (myProject == null) return null;
+    if (myProject == null || myProject.isDefault()) return null;
     return new OpenFileDescriptor(myProject, myFile);
   }
 

platform/diff-impl/src/com/intellij/diff/contents/FileDocumentContentImpl.java

@@ -39,7 +39,7 @@ public class FileDocumentContentImpl extends DocumentContentImpl implements File
   @Nullable
   @Override
   public OpenFileDescriptor getOpenFileDescriptor(int offset) {
-    if (myProject == null) return null;
+    if (myProject == null || myProject.isDefault()) return null;
     return new OpenFileDescriptor(myProject, myFile, offset);
   }
 

platform/platform-impl/src/com/intellij/ide/diff/VirtualFileDiffElement.java

@@ -96,7 +96,7 @@ public class VirtualFileDiffElement extends DiffElement<VirtualFile> {
   @Override
   @Nullable
   public OpenFileDescriptor getOpenFileDescriptor(@Nullable Project project) {
-    if (project == null) return null;
+    if (project == null || project.isDefault()) return null;
     return new OpenFileDescriptor(project, myFile);
   }
 

platform/platform-impl/src/com/intellij/openapi/diff/ex/DiffPanelOptions.java

@@ -59,7 +59,7 @@ public class DiffPanelOptions {
   }
 
   public void showSource(@Nullable OpenFileDescriptor descriptor) {
-    if (descriptor == null || myDiffPanel.getProject() == null) return;
+    if (descriptor == null || myDiffPanel.getProject() == null || myDiffPanel.getProject().isDefault()) return;
     myShowSourcePolicy.showSource(descriptor, myDiffPanel);
   }