fix sprintf WIP

Author: fglock

src/main/java/org/perlonjava/operators/SprintfOperator.java

@@ -69,7 +69,8 @@ public static RuntimeScalar sprintf(RuntimeScalar runtimeScalar, RuntimeList lis
                     charsWritten += formatted.length();
 
                     // Update argument index if not using positional parameters
-                    if (spec.parameterIndex == null && spec.conversionChar != '%') {
+                    // BUT don't update if the specifier was invalid
+                    if (spec.parameterIndex == null && spec.conversionChar != '%' && spec.isValid) {
                         argIndex = updateArgIndex(spec, argIndex);
                     }
                 }
@@ -342,6 +343,9 @@ private static String handleInvalidSpecifier(SprintfFormatParser.FormatSpecifier
             WarnDie.warn(new RuntimeScalar(warningMessage), new RuntimeScalar(""));
         }
 
+        // Don't consume any arguments for invalid specifiers
+        // The caller should NOT update argIndex for invalid formats
+
         return formatOnly + trailing;
     }