Handle whatever reason a platform specific class is in accessible

(some users get security exceptions)

PR:	15421


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@273883 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/util/JavaEnvUtils.java

@@ -125,7 +125,7 @@ public class JavaEnvUtils {
             Class.forName("java.lang.CharSequence");
             javaVersion = JAVA_1_4;
             javaVersionNumber++;
-        } catch (ClassNotFoundException cnfe) {
+        } catch (Throwable t) {
             // swallow as we've hit the max class version that
             // we have
         }