Add community knowledge on AL boolean operators not short-circuiting

AL gives no short-circuit (lazy) evaluation guarantee for and/or/xor —
neither the AL operators nor the boolean operators documentation defines a
lazy evaluation order. LLMs trained on C#, JavaScript, or SQL assume the
left operand guards the right, which produces conditions where a guard
does not protect an unsafe subscript or a field read after a failed Get,
and where an expensive operand is paid on every path.

Adds community/knowledge/performance/boolean-operators-do-not-short-circuit.md
with good/bad AL companions. The guidance prefers nested if when one operand
depends on another, while keeping and/or legitimate for operands that are
independently safe and cheap, so a reviewer does not flag harmless bound
checks. This is the first article in a community performance domain; the
Microsoft performance review leaf skill already sources candidates by domain
across every enabled layer, so no skill change is needed to reach it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

community/knowledge/performance/boolean-operators-do-not-short-circuit.good.al

@@ -0,0 +1,24 @@
+codeunit 50540 "Perf Sample NoShortCircuit Good"
+{
+    procedure ExceedsThreshold(var Thresholds: array[10] of Decimal; Index: Integer; Amount: Decimal): Boolean
+    begin
+        // 'and' is safe here: both operands are cheap and neither depends on the other.
+        if (Index >= 1) and (Index <= ArrayLen(Thresholds)) then
+            // The subscript lives in its own if, so it is never evaluated out of range.
+            if Amount > Thresholds[Index] then
+                exit(true);
+        exit(false);
+    end;
+
+    procedure IsBlockedCustomer(CustomerNo: Code[20]): Boolean
+    var
+        Customer: Record Customer;
+    begin
+        // The cheap test runs first, and the field is read only after Get succeeded.
+        if CustomerNo = '' then
+            exit(false);
+        if not Customer.Get(CustomerNo) then
+            exit(false);
+        exit(Customer.Blocked <> Customer.Blocked::" ");
+    end;
+}