fix: handle missing semicolon in abstract function declarations

When processing malformed PHP code where an abstract function
declaration is missing both the semicolon and curly braces, the
FunctionDeclarationSniff would crash with "Undefined array key -1".

This occurred because findNext(T_SEMICOLON) returns false when no
semicolon is found, and the code attempted to access tokens[false - 1],
which evaluates to tokens[-1].

The fix checks if findNext() returns false and exits early, allowing
other sniffs to report the actual syntax error rather than crashing.

Fixes #3917

Author: dmzoneill

src/Standards/PEAR/Sniffs/Functions/FunctionDeclarationSniff.php

@@ -127,6 +127,11 @@ public function process(File $phpcsFile, $stackPtr)
             // Must be no space before semicolon in abstract/interface methods.
             if ($phpcsFile->getMethodProperties($stackPtr)['has_body'] === false) {
                 $end = $phpcsFile->findNext(T_SEMICOLON, $closeBracket);
+                if ($end === false) {
+                    // Malformed function declaration without semicolon - skip this check.
+                    return;
+                }
+
                 if ($tokens[($end - 1)]['content'] === $phpcsFile->eolChar) {
                     $spaces = 'newline';
                 } else if ($tokens[($end - 1)]['code'] === T_WHITESPACE) {