Slight refactor of CBuffer & CBufLine.

This is in preparation of adding more attributes to a CBufLine. Going
forward, at least savebuf will need access to all of these to properly
serialize buffers.

Basically, instead of relying on `GetLine()` to return `false`, the
caller is now expected to check bounds himself using `Size()`.

modules/savebuff.cpp

@@ -148,9 +148,10 @@ public:
 
 				CString sFile = CRYPT_VERIFICATION_TOKEN;
 
-				unsigned int uIdx = 0;
-				while (Buffer.GetLineFormat(uIdx++, sLine)) {
-					sFile += sLine + "\n";
+				unsigned int uSize = Buffer.Size();
+				for (unsigned int uIdx = 0; uIdx < uSize; uIdx++) {
+					const CBufLine& Line = Buffer.GetBufLine(uIdx);
+					sFile += Line.GetFormat() + "\n";
 				}
 
 				CBlowfish c(m_sPassword, BF_ENCRYPT);