Add array bounds check to fnmatch impl

Author: bjfish

CHANGELOG.md

@@ -37,6 +37,7 @@ Bug fixes:
 * Fixed `#inspect` on broken UTF-8 sequences (#1842, @chrisseaton).
 * `Truffle::Interop.keys` should report methods of String and Symbol (#1817)
 * `Kernel#sprintf` encoding validity has been fixed (#1852, @XrXr).
+* Fixed File.fnmatch causes ArrayIndexOutOfBoundsException (#1845).
 
 Compatibility:
 

src/main/java/org/truffleruby/core/support/IONodes.java

@@ -304,7 +304,7 @@ public static int fnmatch(
                         }
                     }
                     /* failed : try next recursion */
-                    if (ptmp != -1 && stmp != -1 && !(period && string[stmp] == '.')) {
+                    if (ptmp != -1 && stmp != -1 && !(period && stmp < string.length && string[stmp] == '.')) {
                         stmp = nextSlashIndex(string, stmp, send);
                         if (stmp < send) {
                             pat_pos = ptmp;