Fix bug with appending an empty line after a partial line. It should add a...

Fix bug with appending an empty line after a partial line. It should add a blank line but it was a no-op. This made appendScreenToSCrollback push fewer lines than expected and popScrollbackLines would make a mess of things when called later. Also, empty lines would sometimes be missing from the scrollback buffer.

LineBuffer.m

@@ -118,7 +118,13 @@ static char* formatsct(screen_char_t* src, int len, char* dest) {
     if (length > free_space) {
         return NO;
     }
-    if (is_partial) {
+    // There's a bit of an edge case here: if you're appending an empty
+    // non-partial line to a partial line, we need it to append a blank line
+    // after the continued line. In practice this happens because a line is
+    // long but then the wrapped portion is erased and the EOL_SOFT flag stays
+    // behind. It would be really complex to ensure consistency of line-wrapping
+    // flags because the screen contents are changed in so many places.
+    if (is_partial && !(!partial && length == 0)) {
         // append to an existing line
         NSAssert(cll_entries > 0, @"is_partial but has no entries");
         cumulative_line_lengths[cll_entries - 1] += length;

ScreenChar.h

@@ -226,3 +226,6 @@ NSString* ScreenCharArrayToString(screen_char_t* screenChars,
 // Number of chars before a sequence of nuls at the end of the line.
 int EffectiveLineLength(screen_char_t* theLine, int totalLength);
+
+NSString* ScreenCharArrayToStringDebug(screen_char_t* screenChars,
+                                       int lineLength);

ScreenChar.m

@@ -326,6 +326,18 @@ NSString* ScreenCharArrayToString(screen_char_t* screenChars,
                                      freeWhenDone:NO] autorelease];
 }
+NSString* ScreenCharArrayToStringDebug(screen_char_t* screenChars,
+                                       int lineLength) {
+  NSMutableString* result = [NSMutableString stringWithCapacity:lineLength];
+  for (int i = 0; i < lineLength; ++i) {
+    unichar c = screenChars[i].code;
+    if (c != DWC_RIGHT) {
+      [result appendString:ScreenCharToStr(&screenChars[i])];
+    }
+  }
+  return result;
+}
+
 int EffectiveLineLength(screen_char_t* theLine, int totalLength) {
     for (int i = totalLength-1; i >= 0; i--) {
         if (theLine[i].complexChar || theLine[i].code) {