Revert "js: Optimize op.less when right side is always a number"

This reverts commit 36ee6f65de.

src/compiler/jsgen.js

@@ -324,10 +324,9 @@ class JSGenerator {
             if (left.isNeverNumber() || right.isNeverNumber()) {
                 return new TypedInput(`(${left.asString()}.toLowerCase() < ${right.asString()}.toLowerCase())`, TYPE_BOOLEAN);
             }
-            // When the right hand side is known to be a number, we can use >
-            // NaN always returns false in JS's < when compared against a number, just like Scratch.
-            if (right.isAlwaysNumber()) {
-                return new TypedInput(`(${left.asNumberOrNaN()} < ${right.asNumber()})`, TYPE_BOOLEAN);
+            // When both operands are known to be numbers, we can use >
+            if (left.isAlwaysNumber() && right.isAlwaysNumber()) {
+                return new TypedInput(`(${left.asNumber()} < ${right.asNumber()})`, TYPE_BOOLEAN);
             }
             // No compile-time optimizations possible - use fallback method.
             return new TypedInput(`compareLessThan(${left.asUnknown()}, ${right.asUnknown()})`, TYPE_BOOLEAN);