Fix reading zero bytes from EexecFilterDecode

Author: e-zhavoronok

src/main/java/org/verapdf/pd/font/type1/EexecFilterDecode.java

@@ -86,7 +86,13 @@ public EexecFilterDecode(ASInputStream stream, boolean isCharstring) throws IOEx
     public int read(byte[] buffer, int size) throws IOException {
         int bytesRead = this.feedBuffer(bytesToDiscard + size);
         int res = bytesRead - bytesToDiscard;
-        if (bytesRead <= 0) {
+        if (bytesRead < 0) {
+            return -1;
+        }
+        else if (size == 0) {
+            return 0;
+        }
+        else if (bytesRead == 0) {
             return -1;
         }
         for (int i = 0; i < bytesRead; ++i) {