fix: handle line offset in block quote correctly (#17)

Author: galaxian85

lib/rules_block/blockquote.js

@@ -278,12 +278,17 @@ module.exports = function blockquote(state, startLine, endLine, silent) {
   for (i = 0; i < oldTShift.length; i++) {
     const lineNumber = i + startLine;
     if (state.lineOffsets[lineNumber] === null) {
-      state.lineOffsets[lineNumber] = totalLineOffset;
+      if (i === 0) {
+        // first line of blockquote
+        state.lineOffsets[lineNumber] = 0;
+        continue;
+      }
       if (isNotEmptyLine(state, lineNumber)) {
         totalLineOffset += calcLineOffset(state, lineNumber);
       } else {
         totalLineOffset = 0;
       }
+      state.lineOffsets[lineNumber] = totalLineOffset;
     }
 
     state.bMarks[lineNumber] = oldBMarks[i];