Fix script test handling of empty scripts

Previously an empty script would evaluate to OP_0

src/test/data/script_invalid.json

@@ -1,8 +1,18 @@
 [
+["", "DEPTH",   "Test the test: we should have an empty stack after scriptSig evaluation"],
+["  ", "DEPTH", "and multiple spaces should not change that."],
+["   ", "DEPTH"],
+["    ", "DEPTH"],
+
 ["", ""],
 ["", "NOP"],
+["", "NOP DEPTH"],
 ["NOP", ""],
+["NOP", "DEPTH"],
 ["NOP","NOP"],
+["NOP","NOP DEPTH"],
+
+["DEPTH", ""],
 
 ["0x4c01","0x01 NOP", "PUSHDATA1 with not enough bytes"],
 ["0x4d0200ff","0x01 NOP", "PUSHDATA2 with not enough bytes"],

src/test/data/script_valid.json

@@ -1,4 +1,16 @@
 [
+["", "DEPTH 0 EQUAL",   "Test the test: we should have an empty stack after scriptSig evaluation"],
+["  ", "DEPTH 0 EQUAL", "and multiple spaces should not change that."],
+["   ", "DEPTH 0 EQUAL"],
+["    ", "DEPTH 0 EQUAL"],
+["1 2", "2 EQUALVERIFY 1 EQUAL", "Similarly whitespace around and between symbols"],
+["1  2", "2 EQUALVERIFY 1 EQUAL"],
+["  1  2", "2 EQUALVERIFY 1 EQUAL"],
+["1  2  ", "2 EQUALVERIFY 1 EQUAL"],
+["  1  2  ", "2 EQUALVERIFY 1 EQUAL"],
+
+["1", ""],
+
 ["0x01 0x0b", "11 EQUAL", "push 1 byte"],
 ["0x02 0x417a", "'Az' EQUAL"],
 ["0x4b 0x417a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a7a",

src/test/script_tests.cpp

@@ -63,7 +63,11 @@ ParseScript(string s)
 
     BOOST_FOREACH(string w, words)
     {
-        if (all(w, is_digit()) ||
+        if (w.size() == 0)
+        {
+            // Empty string, ignore. (boost::split given '' will return one word)
+        }
+        else if (all(w, is_digit()) ||
             (starts_with(w, "-") && all(string(w.begin()+1, w.end()), is_digit())))
         {
             // Number