Fix NPE when accessing xcodeProperties (#5714)

The problem occured when a user:
- imported a project with empty targets list in projectview OR
- ran incremental sync without any changes in targets list

closes #5695

cpp/src/com/google/idea/blaze/cpp/BlazeConfigurationResolverResult.java

@@ -105,7 +105,7 @@ static class Builder {
         ImmutableMap.of();
     ImmutableMap<CToolchainIdeInfo, BlazeCompilerSettings> compilerSettings = ImmutableMap.of();
     ImmutableSet<File> validHeaderRoots = ImmutableSet.of();
-    Optional<XcodeCompilerSettings> xcodeSettings;
+    Optional<XcodeCompilerSettings> xcodeSettings = Optional.empty();
     private ImmutableMap<String, String> setTargetToVersionMap;
 
     public Builder() {}