Fix ChangeUtil for non-MultiTextEdit conversion

[Eskibear]

Signed-off-by: Yan Zhang [email protected]

Reason

When I was passing a simple InsertEdit, this method failed to process the edit as it had no children.

Change

• For MultiTextEdit, process its children; otherwise process the edit itself.
• Remove the zero-length check as it's already guarded by the for-loop. There's also no NPE risk as TextEdit.getChildren() always returns a non-null array.

[Eskibear]

java.lang.AssertionError: No pom.xml errors were found expected:<3> but was:<6>
at org.eclipse.jdt.ls.core.internal.handlers.WorkspaceDiagnosticsHandlerTest.testResetPomDiagnostics(WorkspaceDiagnosticsHandlerTest.java:400)

CI failed with above case, which passed in my local environment. And the change should not affect the case. Close & reopen the PR to retrigger it.