ControlStructures/AssignmentInCondition: prevent fatal error during l…

…ive coding

```
Fatal error: Uncaught TypeError: SlevomatCodingStandard\Sniffs\ControlStructures\AssignmentInConditionSniff::processCondition(): Argument slevomat#3 ($parenthesisCloser) must be of type int, null given, called in path\to\SlevomatCodingStandard\Sniffs\ControlStructures\AssignmentInConditionSniff.php on line 56 and defined in path\to\SlevomatCodingStandard\Sniffs\ControlStructures\AssignmentInConditionSniff.php:59
Stack trace:
#0 path\to\SlevomatCodingStandard\Sniffs\ControlStructures\AssignmentInConditionSniff.php(56): SlevomatCodingStandard\Sniffs\ControlStructures\AssignmentInConditionSniff->processCondition(Object(PHP_CodeSniffer\Files\LocalFile), 100, NULL, 'if')
slevomat#1 D:\000_GitHub\PHPCS\PHP_CodeSniffer\src\Files\File.php(509): SlevomatCodingStandard\Sniffs\ControlStructures\AssignmentInConditionSniff->process(Object(PHP_CodeSniffer\Files\LocalFile), 99)
slevomat#2 D:\000_GitHub\PHPCS\PHP_CodeSniffer\src\Files\LocalFile.php(92): PHP_CodeSniffer\Files\File->process()
slevomat#3 D:\000_GitHub\PHPCS\PHP_CodeSniffer\src\Runner.php(632): PHP_CodeSniffer\Files\LocalFile->process()
slevomat#4 D:\000_GitHub\PHPCS\PHP_CodeSniffer\src\Runner.php(438): PHP_CodeSniffer\Runner->processFile(Object(PHP_CodeSniffer\Files\LocalFile))
slevomat#5 D:\000_GitHub\PHPCS\PHP_CodeSniffer\src\Runner.php(116): PHP_CodeSniffer\Runner->run()
slevomat#6 D:\000_GitHub\PHPCS\PHP_CodeSniffer\bin\phpcs(18): PHP_CodeSniffer\Runner->runPHPCS()
slevomat#7 {main}
  thrown in path\to\SlevomatCodingStandard\Sniffs\ControlStructures\AssignmentInConditionSniff.php on line 59
```

SlevomatCodingStandard/Sniffs/ControlStructures/AssignmentInConditionSniff.php

@@ -53,6 +53,11 @@ public function process(File $phpcsFile, $conditionStartPointer): void
 			$parenthesisCloser = $token['parenthesis_closer'];
 			$type = $token['code'] === T_IF ? 'if' : 'elseif';
 		}
+
+		if (isset($parenthesisOpener, $parenthesisCloser) === false) {
+			return;
+		}
+
 		$this->processCondition($phpcsFile, $parenthesisOpener, $parenthesisCloser, $type);
 	}
 

tests/Sniffs/ControlStructures/data/noAssignmentsInConditions.php

@@ -43,3 +43,7 @@
 do {
 
 } while ($foo === 5);
+
+// Live coding/parse error.
+// This must be the last test in the file.
+if ($a = 1