some additional comments, remove apt-get from clang jobs, better test titles

lib/decompress/zstd_decompress.c

@@ -2059,7 +2059,7 @@ size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inB
                     if (ZSTD_isError(decompressedSize)) return decompressedSize;
                     DEBUGLOG(4, "shortcut to single-pass ZSTD_decompress_usingDDict()")
                     ip = istart + cSize;
-                    op = op ? op + decompressedSize : op;
+                    op = op ? op + decompressedSize : op; /* can occur if frameContentSize = 0 (empty frame) */
                     zds->expected = 0;
                     zds->streamStage = zdss_init;
                     someMoreWork = 0;
@@ -2194,7 +2194,7 @@ size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inB
                         zds->outStart = zds->outEnd = 0;
                     }
                     break;
-            }}
+            }   }
             /* cannot complete flush */
             someMoreWork = 0;
             break;