Improve worst-case behavior of CScript::FindAndDelete

Thanks to Sergio Lerner for identifying this issue and suggesting this kind of solution.

src/script/script.h

@@ -570,17 +570,26 @@ public:
         int nFound = 0;
         if (b.empty())
             return nFound;
-        iterator pc = begin();
+        CScript result;
+        iterator pc = begin(), pc2 = begin();
         opcodetype opcode;
         do
         {
+            result.insert(result.end(), pc2, pc);
             while (static_cast<size_t>(end() - pc) >= b.size() && std::equal(b.begin(), b.end(), pc))
             {
-                pc = erase(pc, pc + b.size());
+                pc = pc + b.size();
                 ++nFound;
             }
+            pc2 = pc;
         }
         while (GetOp(pc, opcode));
+
+        if (nFound > 0) {
+            result.insert(result.end(), pc2, end());
+            *this = result;
+        }
+
         return nFound;
     }
     int Find(opcodetype op) const