Fix crash in OS::execute on FreeBSD

As spotted by @robfram, closes #15288.
Also reviewed other uses of `if (String.find(.*))` for potential similar mistakes, found a wrong (and useless) one in ScriptEditorDialog.

drivers/unix/os_unix.cpp

@@ -298,7 +298,7 @@ Error OS_Unix::execute(const String &p_path, const List<String> &p_arguments, bo
 		args.push_back(0);
 
 #ifdef __FreeBSD__
-		if (p_path.find("/")) {
+		if (p_path.find("/") != -1) {
 			// exec name contains path so use it
 			execv(p_path.utf8().get_data(), &args[0]);
 		} else {

editor/editor_node.cpp

@@ -4423,7 +4423,7 @@ void EditorNode::_dropped_files(const Vector<String> &p_files, int p_screen) {
 	for (int i = 0; i < p_files.size(); i++) {
 
 		String from = p_files[i];
-		if (!ResourceFormatImporter::get_singleton()->can_be_imported(from) && (just_copy.find(from.get_extension().to_lower()) < 0)) {
+		if (!ResourceFormatImporter::get_singleton()->can_be_imported(from) && (just_copy.find(from.get_extension().to_lower()) != -1)) {
 			continue;
 		}
 		String to = to_path.plus_file(from.get_file());

editor/script_create_dialog.cpp

@@ -232,7 +232,7 @@ void ScriptCreateDialog::_lang_changed(int l) {
 	String path = file_path->get_text();
 	String extension = "";
 	if (path != "") {
-		if (path.find(".") >= 0) {
+		if (path.find(".") != -1) {
 			extension = path.get_extension();
 		}
 
@@ -359,16 +359,14 @@ void ScriptCreateDialog::_path_changed(const String &p_path) {
 		return;
 	}
 
-	if (p.find("/") || p.find("\\")) {
-		DirAccess *d = DirAccess::create(DirAccess::ACCESS_RESOURCES);
-		if (d->change_dir(p.get_base_dir()) != OK) {
-			_msg_path_valid(false, TTR("Invalid base path"));
-			memdelete(d);
-			_update_dialog();
-			return;
-		}
+	DirAccess *d = DirAccess::create(DirAccess::ACCESS_RESOURCES);
+	if (d->change_dir(p.get_base_dir()) != OK) {
+		_msg_path_valid(false, TTR("Invalid base path"));
 		memdelete(d);
+		_update_dialog();
+		return;
 	}
+	memdelete(d);
 
 	/* Does file already exist */
 

scene/gui/color_picker.cpp

@@ -209,6 +209,7 @@ Color ColorPicker::get_pick_color() const {
 }
 
 void ColorPicker::add_preset(const Color &p_color) {
+
 	if (presets.find(p_color)) {
 		presets.move_to_back(presets.find(p_color));
 	} else {