Fix #4011 - prevent mixed assignment in loop

src/Psalm/Internal/Type/SimpleAssertionReconciler.php

@@ -531,7 +531,7 @@ class SimpleAssertionReconciler extends \Psalm\Type\Reconciler
 
         $failed_reconciliation = 2;
 
-        return Type::getMixed();
+        return Type::getEmpty();
     }
 
     /**

tests/Loop/WhileTest.php

@@ -451,7 +451,19 @@ class WhileTest extends \Psalm\Tests\TestCase
 
                         return $elements;
                     }',
-            ]
+            ],
+            'reconcilePositiveInt' => [
+                '<?php
+                    $counter = 0;
+
+                    while (rand(0, 1)) {
+                        if ($counter > 0) {
+                            $counter = $counter - 1;
+                        } else {
+                            $counter = $counter + 1;
+                        }
+                    }'
+            ],
         ];
     }