Fix AbstractAirspace setDragEnabled honoring input

[arpitjain099]

This fixes a logic bug in AbstractAirspace where setDragEnabled(boolean enabled) always set the internal field to true and ignored the method argument.

Changes:

• set dragEnabled to the passed enabled value in AbstractAirspace
• add a focused JUnit regression test class that verifies both false and true paths

Files:

• src/gov/nasa/worldwind/render/airspaces/AbstractAirspace.java
• test/gov/nasa/worldwind/render/airspaces/AbstractAirspaceTest.java

Fixes #240

Verification:

• I validated the logic change by adding JUnit coverage for both branches.
• I could not run the test suite in this environment because Java runtime/compiler tools are not installed (java and javac are unavailable).