[fix] Incremental DT with no frames #841

Job	Run time
Coverage (STP)	37m 58s
clang-format	5m 33s
Linux (LLVM 14)	22m 21s
Coverage (Z3)	40m 29s
Linux (LLVM 13)	20m 10s
Docker	11m 12s
macOS	10m 26s
Linux (LLVM 12)	19m 37s
Linux (LLVM 11, Doxygen)	19m 8s
Linux (LLVM 10)	14m 42s
Linux (LLVM 9)	14m 15s
Linux (ASan)	49m 44s
Linux (UBSan)	56m 56s
Linux (MSan)	51m 16s
Linux (Z3 only)	19m 44s
Linux (metaSMT)	34m 53s
Linux (STP master)	14m 18s
Linux (Latest klee-uclibc)	15m 38s
Linux (Asserts disabled)	14m 39s
Linux (No TCMalloc, optimised runtime)	14m 14s
	8h 7m 13s

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