Fix NullPointerException in MavenSelectionHintsTask

[jglick]

Fixes #4993 by code inspection, amending mistake introduced in #3833. Both call sites require the result to be non-null:

netbeans/java/maven.hints/src/org/netbeans/modules/maven/hints/pom/MavenSelectionHintsTask.java

Lines 68 to 69 in 67393d2

	List<ErrorDescription> errors = computeErrors(result, ss, se, cursorEvent.getCaretOffset());
	HintsController.setErrors(result.getPomFile(), PomModelUtils.LAYER_POM_SELECTION, errors);

netbeans/ide/spi.editor.hints/src/org/netbeans/spi/editor/hints/HintsController.java

Lines 72 to 75 in 67393d2

	public static void setErrors(final @NonNull FileObject file, @NonNull final String layer, @NonNull Collection<? extends ErrorDescription> errors) {
	Parameters.notNull("file", file);
	Parameters.notNull("layer", layer);
	Parameters.notNull("errors", errors);

netbeans/java/maven.hints/src/org/netbeans/modules/maven/hints/pom/LspMavenErrorProvider.java

Lines 77 to 81 in 67393d2

	errors = MavenSelectionHintsTask.computeErrors(result, context.getOffset(), context.getOffset(), context.getOffset());
	} else {
	errors = new ArrayList<>();
	}
	errors.addAll(PomModelUtils.findHints(result.getProjectModel(), p));

[mbien]

restarting CI for maven tests due to label change