Fix display of file content with empty line at beginning

In the previous solution, all files that would start with an empty line were not shown. This commit fixes that issue.

Regresses 7576d1e

Author: MrSerth

app/assets/javascripts/editor/editor.js

@@ -281,7 +281,8 @@ var CodeOceanEditor = {
             this.setActiveFile($(element).parent().data('filename'), file_id);
 
             const full_lines = content.text().split(/\n/);
-            if (full_lines.length >= 1 && full_lines[0] !== "") {
+            // Prevent inserting a single empty line, as the editor already contains one by default.
+            if (full_lines.length > 1 || (full_lines.length === 1 && full_lines[0] !== "")) {
                 document.insertFullLines(0, full_lines);
                 // remove last (empty) that is there by default line
                 document.removeFullLines(document.getLength() - 1, document.getLength() - 1);