Fix PHPStan error

Author: piurafunk

src/Parser/Header.php

@@ -80,23 +80,36 @@ public function getName(): string
         return rtrim($str, "\0");
     }
 
+    /**
+     * @return int<1, max>
+     */
     public function getSize(): int
     {
         if (array_key_exists('size', $this->pax)) {
-            return (int)$this->pax['size'];
+            $size = (int)$this->pax['size'];
+        } else {
+            $size = rtrim(substr($this->content, 124, 12));
+            if (preg_match('/^[0-7]+$/D', $size) !== 1) {
+                throw new InvalidArchiveFormatException(
+                    sprintf(
+                        "Invalid Tar header format, file size must be octal number, '%s' got instead",
+                        $size
+                    )
+                );
+            }
+            $size = (int)octdec($size);
         }
 
-        $str = rtrim(substr($this->content, 124, 12));
-        if (preg_match('/^[0-7]+$/D', $str) !== 1) {
+        if ($size < 1) {
             throw new InvalidArchiveFormatException(
                 sprintf(
-                    "Invalid Tar header format, file size must be octal number, '%s' got instead",
-                    $str
+                    "Invalid Tar header format, file size must be positive number, '%s' got instead",
+                    $size
                 )
             );
         }
 
-        return (int)octdec($str);
+        return $size;
     }
 
     public function mergePaxHeader(Header $header): void