Revert most of PR #168

i.e of the commit f436c30.

It added bunch of checks all over the place, but most of them
shouldn't be needed: If they are true, our internal state is
already broken. In other words, those checks are hiding real bugs
and making debugging harder.

Hopefully the underlying bugs are already fixed in some of previous
commits addressing some fuzzing issues, like these:

 * d775b51
 * c6942ef

src/md4c.c

@@ -2344,7 +2344,7 @@ md_is_inline_link_spec(MD_CTX* ctx, const MD_LINE* lines, int n_lines,
     /* Optional whitespace followed with final ')'. */
     while(off < lines[line_index].end  &&  ISWHITESPACE(off))
         off++;
-    if (off >= lines[line_index].end  &&  (off >= ctx->size || ISNEWLINE(off))) {
+    if(off >= lines[line_index].end  &&  ISNEWLINE(off)) {
         line_index++;
         if(line_index >= n_lines)
             return FALSE;
@@ -2657,11 +2657,8 @@ md_rollback(MD_CTX* ctx, int opener_index, int closer_index, int how)
     for(i = OPENERS_CHAIN_FIRST; i < OPENERS_CHAIN_LAST+1; i++) {
         MD_MARKCHAIN* chain = &ctx->mark_chains[i];
 
-        while(chain->tail >= opener_index) {
-            int same = chain->tail == opener_index;
+        while(chain->tail >= opener_index)
             chain->tail = ctx->marks[chain->tail].prev;
-            if (same) break;
-        }
 
         if(chain->tail >= 0)
             ctx->marks[chain->tail].next = -1;
@@ -3965,7 +3962,7 @@ md_analyze_permissive_email_autolink(MD_CTX* ctx, int mark_index)
     OFF end = opener->end;
     int dot_count = 0;
 
-    MD_ASSERT(opener->ch == _T('@'));
+    MD_ASSERT(CH(beg) == _T('@'));
 
     /* Scan for name before '@'. */
     while(beg > 0  &&  (ISALNUM(beg-1) || ISANYOF(beg-1, _T(".-_+"))))
@@ -3990,7 +3987,7 @@ md_analyze_permissive_email_autolink(MD_CTX* ctx, int mark_index)
      * length so all the contents becomes the link text. */
     closer_index = mark_index + 1;
     closer = &ctx->marks[closer_index];
-    if (closer->ch != 'D') return;
+    MD_ASSERT(closer->ch == 'D');
 
     opener->beg = beg;
     opener->end = beg;
@@ -4290,7 +4287,7 @@ md_process_inlines(MD_CTX* ctx, const MD_LINE* lines, int n_lines)
                     dest_mark = opener+1;
                     MD_ASSERT(dest_mark->ch == 'D');
                     title_mark = opener+2;
-                    if (title_mark->ch != 'D') break;
+                    MD_ASSERT(title_mark->ch == 'D');
 
                     MD_CHECK(md_enter_leave_span_a(ctx, (mark->ch != ']'),
                                 (opener->ch == '!' ? MD_SPAN_IMG : MD_SPAN_A),
@@ -5542,7 +5539,7 @@ md_is_html_block_end_condition(MD_CTX* ctx, OFF beg, OFF* p_end)
         case 6:     /* Pass through */
         case 7:
             *p_end = beg;
-            return (beg >= ctx->size || ISNEWLINE(beg) ? ctx->html_block_type : FALSE);
+            return (ISNEWLINE(beg) ? ctx->html_block_type : FALSE);
 
         default:
             MD_UNREACHABLE();
@@ -6144,9 +6141,8 @@ md_analyze_line(MD_CTX* ctx, OFF beg, OFF* p_end,
                 task_container->is_task = TRUE;
                 task_container->task_mark_off = tmp + 1;
                 off = tmp + 3;
-                while(off < ctx->size && ISWHITESPACE(off))
+                while(ISWHITESPACE(off))
                     off++;
-                if (off == ctx->size) break;
                 line->beg = off;
             }
         }