Keep going even when function doesn’t exist

src/Psalm/Internal/Analyzer/Statements/Expression/Call/FunctionCallAnalyzer.php

@@ -263,7 +263,7 @@ class FunctionCallAnalyzer extends \Psalm\Internal\Analyzer\Statements\Expressio
                         $is_maybe_root_function
                     ) === false
                     ) {
-                        return false;
+                        return;
                     }
                 }
             } else {

tests/IssueSuppressionTest.php

@@ -89,6 +89,15 @@ class IssueSuppressionTest extends TestCase
                         strlen("a", "b");
                     }'
             ],
+            'suppressUndefinedFunction' => [
+                '<?php
+                    function verify_return_type(): DateTime {
+                        /** @psalm-suppress UndefinedFunction */
+                        unknown_function_call();
+
+                        return new DateTime();
+                    }',
+            ],
         ];
     }