- check paths are not empty strings before making blend file paths absolute or relative.

- when saving blend file with 'Remap Relative' enabled, don't try make paths absolute if the internal filename is invalid.
- use case insensitive path comparison on windows when checking if path remapping is needed & for comparing next/prev dirs in the file selector.

source/blender/blenlib/intern/bpath.c

@@ -700,6 +700,11 @@ void makeFilesRelative(Main *bmain, const char *basedir, ReportList *reports) {
 	/* be sure there is low chance of the path being too short */
 	char filepath_relative[(FILE_MAXDIR * 2) + FILE_MAXFILE];
 
+	if(basedir[0] == '\0') {
+		printf("makeFilesRelative: basedir='', this is a bug\n");
+		return;
+	}
+
 	BLI_bpathIterator_init(&bpi, bmain, basedir, 0);
 	while (!BLI_bpathIterator_isDone(bpi)) {
 		BLI_bpathIterator_getPath(bpi, filepath);
@@ -751,7 +756,10 @@ void makeFilesAbsolute(Main *bmain, const char *basedir, ReportList *reports)
 	/* be sure there is low chance of the path being too short */
 	char filepath_absolute[(FILE_MAXDIR * 2) + FILE_MAXFILE];
 
-	BLI_assert(basedir[0] != '\0');
+	if(basedir[0] == '\0') {
+		printf("makeFilesAbsolute: basedir='', this is a bug\n");
+		return;
+	}
 
 	BLI_bpathIterator_init(&bpi, bmain, basedir, 0);
 	while (!BLI_bpathIterator_isDone(bpi)) {

source/blender/blenloader/intern/writefile.c

@@ -2547,11 +2547,19 @@ int BLO_write_file(Main *mainvar, const char *filepath, int write_flags, ReportL
 		BLI_cleanup_dir(mainvar->name, dir1);
 		BLI_cleanup_dir(mainvar->name, dir2);
 
-		if(strcmp(dir1, dir2)==0)
+		if(BLI_path_cmp(dir1, dir2)==0) {
 			write_flags &= ~G_FILE_RELATIVE_REMAP;
-		else
+		}
+		else {
+			if(G.relbase_valid) {
+				/* blend may not have been saved before. Tn this case
+				 * we should not have any relative paths, but if there
+				 * is somehow, an invalid or empty G.main->name it will
+				 * print an error, dont try make the absolute in this case. */
 				makeFilesAbsolute(mainvar, G.main->name, NULL);
 			}
+		}
+	}
 
 	BLI_make_file_string(G.main->name, userfilename, BLI_get_folder_create(BLENDER_USER_CONFIG, NULL), BLENDER_STARTUP_FILE);
 	write_user_block= (BLI_path_cmp(filepath, userfilename) == 0);

source/blender/editors/space_file/filelist.c

@@ -433,7 +433,7 @@ void folderlist_pushdir(ListBase* folderlist, const char *dir)
 
 	// check if already exists
 	if(previous_folder && previous_folder->foldername){
-		if(! strcmp(previous_folder->foldername, dir)){
+		if(BLI_path_cmp(previous_folder->foldername, dir)==0){
 			return;
 		}
 	}