tree-wide: port everything over to fflush_and_check()

Some places invoked fflush() directly with their own manual error
checking, let's unify all that by using fflush_and_check().

This also unifies the general error paths of fflush()+rename() file
writers.

src/libsystemd/sd-bus/bus-dump.c

@@ -551,9 +551,8 @@ int bus_pcap_header(size_t snaplen, FILE *f) {
         hdr.snaplen = (uint32_t) snaplen;
 
         fwrite(&hdr, 1, sizeof(hdr), f);
-        fflush(f);
 
-        return 0;
+        return fflush_and_check(f);
 }
 
 int bus_message_pcap_frame(sd_bus_message *m, size_t snaplen, FILE *f) {
@@ -598,7 +597,5 @@ int bus_message_pcap_frame(sd_bus_message *m, size_t snaplen, FILE *f) {
                 snaplen -= w;
         }
 
-        fflush(f);
-
-        return 0;
+        return fflush_and_check(f);
 }

src/libsystemd/sd-bus/bus-introspect.c

@@ -179,10 +179,10 @@ int introspect_finish(struct introspect *i, sd_bus *bus, sd_bus_message *m, sd_b
         assert(reply);
 
         fputs("</node>\n", i->f);
-        fflush(i->f);
 
-        if (ferror(i->f))
-                return -ENOMEM;
+        r = fflush_and_check(i->f);
+        if (r < 0)
+                return r;
 
         r = sd_bus_message_new_method_return(m, &q);
         if (r < 0)
@@ -204,8 +204,6 @@ void introspect_free(struct introspect *i) {
         if (i->f)
                 fclose(i->f);
 
-        if (i->introspection)
-                free(i->introspection);
-
+        free(i->introspection);
         zero(*i);
 }

src/libsystemd/sd-bus/bus-match.c

@@ -914,6 +914,7 @@ char *bus_match_to_string(struct bus_match_component *components, unsigned n_com
         char *buffer = NULL;
         size_t size = 0;
         unsigned i;
+        int r;
 
         if (n_components <= 0)
                 return strdup("");
@@ -942,8 +943,8 @@ char *bus_match_to_string(struct bus_match_component *components, unsigned n_com
                 fputc('\'', f);
         }
 
-        fflush(f);
-        if (ferror(f))
+        r = fflush_and_check(f);
+        if (r < 0)
                 return NULL;
 
         return buffer;

src/libsystemd/sd-device/device-private.c

@@ -1082,12 +1082,10 @@ int device_update_db(sd_device *device) {
         return 0;
 
 fail:
-        log_error_errno(r, "failed to create %s file '%s' for '%s'", has_info ? "db" : "empty",
-                        path, device->devpath);
-        unlink(path);
-        unlink(path_tmp);
+        (void) unlink(path);
+        (void) unlink(path_tmp);
 
-        return r;
+        return log_error_errno(r, "failed to create %s file '%s' for '%s'", has_info ? "db" : "empty", path, device->devpath);
 }
 
 int device_delete_db(sd_device *device) {