Use be_control_look != NULL everywhere in the Interface Kit.

Should not be a functional change. It is not in the Haiku Coding Guidelines but
I feel like 'if (object != NULL)' is generally preferred to 'if (object)', plus
in this case of be_control_look that is the more common style.

src/kits/interface/BMCPrivate.cpp

@@ -407,7 +407,7 @@ _BMCMenuBar_::_Init(bool setMaxContentWidth)
 	bottom--;
 #endif
 
-	if (be_control_look)
+	if (be_control_look != NULL)
 		left = right = be_control_look->DefaultLabelSpacing();
 
 	SetItemMargins(left, top, right + fShowPopUpMarker ? 10 : 0, bottom);

src/kits/interface/CheckBox.cpp

@@ -96,7 +96,7 @@ BCheckBox::Archive(BMessage *archive, bool deep) const
 void
 BCheckBox::Draw(BRect updateRect)
 {
-	if (be_control_look) {
+	if (be_control_look != NULL) {
 		rgb_color base = ui_color(B_PANEL_BACKGROUND_COLOR);
 
 		uint32 flags = be_control_look->Flags(this);

src/kits/interface/RadioButton.cpp

@@ -89,7 +89,7 @@ BRadioButton::Draw(BRect updateRect)
 	font_height fontHeight;
 	GetFontHeight(&fontHeight);
 
-	if (be_control_look) {
+	if (be_control_look != NULL) {
 		rgb_color base = ui_color(B_PANEL_BACKGROUND_COLOR);
 
 		uint32 flags = be_control_look->Flags(this);

src/kits/interface/ScrollBar.cpp

@@ -1081,7 +1081,7 @@ BScrollBar::Draw(BRect updateRect)
 		}
 
 		// fill the clickable surface of the thumb
-		if (be_control_look) {
+		if (be_control_look != NULL) {
 			be_control_look->DrawButtonBackground(this, rect, updateRect,
 				normal, 0, BControlLook::B_ALL_BORDERS, fOrientation);
 		} else {

src/kits/interface/Slider.cpp

@@ -1000,7 +1000,7 @@ BSlider::DrawHashMarks()
 	BRect frame = HashMarksFrame();
 	BView* view = OffscreenView();
 
-	if (be_control_look) {
+	if (be_control_look != NULL) {
 		rgb_color base = ui_color(B_PANEL_BACKGROUND_COLOR);
 		uint32 flags = be_control_look->Flags(this);
 		be_control_look->DrawSliderHashMarks(view, frame, frame, base,

src/kits/interface/StatusBar.cpp

@@ -574,7 +574,7 @@ BStatusBar::SetTo(float value, const char* text, const char* trailingText)
 	}
 
 	// TODO: Ask the BControlLook in the first place about dirty rect.
-	if (be_control_look)
+	if (be_control_look != NULL)
 		update.InsetBy(-1, -1);
 
 	Invalidate(update);

src/kits/interface/TextInput.cpp

@@ -174,7 +174,7 @@ _BTextInput_::AlignTextRect()
 	float vInset = max_c(1, floorf((textRect.Height() - LineHeight(0)) / 2.0));
 	float hInset = 2;
 
-	if (be_control_look)
+	if (be_control_look != NULL)
 		hInset = be_control_look->DefaultLabelSpacing();
 
 	textRect.InsetBy(hInset, vInset);