Fix issue 11576.

std/algorithm.d

@@ -8139,8 +8139,17 @@ if (s != SwapStrategy.stable
         if (blackouts[right].pos + blackouts[right].len >= range.length)
         {
             range.popBackN(blackouts[right].len);
-            --right;
-            continue;
+
+            // Since right is unsigned, we must check for this case, otherwise
+            // we might turn it into size_t.max and the loop condition will not
+            // fail when it should.
+            if (right > 0)
+            {
+                --right;
+                continue;
+            }
+            else
+                break;
         }
         // Advance to next blackout on the left
         assert(blackouts[left].pos >= steps);
@@ -8266,6 +8275,14 @@ unittest
             == [0, 9, 8, 7, 4, 5]);
 }
 
+unittest
+{
+    // Issue 11576
+    auto arr = [1,2,3];
+    arr = arr.remove!(SwapStrategy.unstable)(2);
+    assert(arr == [1,2]);
+}
+
 /**
 Reduces the length of the bidirectional range $(D range) by removing
 elements that satisfy $(D pred). If $(D s = SwapStrategy.unstable),