Request Handler minor improvements (#20)

Author: omarzl

Examples/BazelXCBBuildService/Sources/RequestHandler.swift

@@ -144,6 +144,7 @@ final class RequestHandler: HybridXCBBuildServiceRequestHandler {
             let session = message.sessionHandle
 
             // Reset in case we decide not to build
+            sessionBazelBuilds[session]?.cancel()
             sessionBazelBuilds[session] = nil
 
             handleBazelTargets(session: session) { baseEnvironment, bazelTargets, xcodeBuildVersion in