repl,readline: refactor for simplicity

This just refactors code without changing the behavior. Especially
the REPL code is difficult to read and deeply indented. This reduces
the indentation to improve that.

lib/readline.js

@@ -505,41 +505,43 @@ Interface.prototype._tabComplete = function(lastKeypressWasTab) {
       return;
     }
 
-    const completions = rv[0];
-    const completeOn = rv[1];  // The text that was completed
-    if (completions && completions.length) {
-      // Apply/show completions.
-      if (lastKeypressWasTab) {
-        self._writeToOutput('\r\n');
-        const width = completions.reduce(function completionReducer(a, b) {
-          return a.length > b.length ? a : b;
-        }).length + 2;  // 2 space padding
-        let maxColumns = MathFloor(self.columns / width);
-        if (!maxColumns || maxColumns === Infinity) {
-          maxColumns = 1;
-        }
-        let group = [];
-        for (let i = 0; i < completions.length; i++) {
-          const c = completions[i];
-          if (c === '') {
-            handleGroup(self, group, width, maxColumns);
-            group = [];
-          } else {
-            group.push(c);
-          }
-        }
-        handleGroup(self, group, width, maxColumns);
-      }
+    // Result and the text that was completed.
+    const [completions, completeOn] = rv;
+
+    if (!completions || completions.length === 0) {
+      return;
+    }
 
-      // If there is a common prefix to all matches, then apply that portion.
-      const f = completions.filter((e) => e);
-      const prefix = commonPrefix(f);
-      if (prefix.length > completeOn.length) {
-        self._insertString(prefix.slice(completeOn.length));
+    // Apply/show completions.
+    if (lastKeypressWasTab) {
+      self._writeToOutput('\r\n');
+      const width = completions.reduce((a, b) => {
+        return a.length > b.length ? a : b;
+      }).length + 2;  // 2 space padding
+      let maxColumns = MathFloor(self.columns / width);
+      if (!maxColumns || maxColumns === Infinity) {
+        maxColumns = 1;
       }
+      let group = [];
+      for (const c of completions) {
+        if (c === '') {
+          handleGroup(self, group, width, maxColumns);
+          group = [];
+        } else {
+          group.push(c);
+        }
+      }
+      handleGroup(self, group, width, maxColumns);
+    }
 
-      self._refreshLine();
+    // If there is a common prefix to all matches, then apply that portion.
+    const f = completions.filter((e) => e);
+    const prefix = commonPrefix(f);
+    if (prefix.length > completeOn.length) {
+      self._insertString(prefix.slice(completeOn.length));
     }
+
+    self._refreshLine();
   });
 };