Bug 16638 – segfault if a single lib is passed without sources

dmd -lib blah.a segfaults. blah.a doesn't have to exist. * thread #1: tid = 0x878e, 0x00000001000e8408 dmd`D4ddmd3lib7Library11setFilenameMFPxaPxaZv + 136 at lib.d:89, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0) frame #0: 0x00000001000e8408 dmd`D4ddmd3lib7Library11setFilenameMFPxaPxaZv + 136 at lib.d:89 86 if (!arg || !*arg) 87 { 88 // Generate lib file name from first obj name -> 89 const(char)* n = (*global.params.objfiles)[0]; 90 n = FileName.name(n); 91 arg = FileName.forceExt(n, global.lib_ext); 92 } (lldb) bt * thread #1: tid = 0x878e, 0x00000001000e8408 dmd`D4ddmd3lib7Library11setFilenameMFPxaPxaZv + 136 at lib.d:89, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0) * frame #0: 0x00000001000e8408 dmd`D4ddmd3lib7Library11setFilenameMFPxaPxaZv + 136 at lib.d:89 frame #1: 0x00000001000ed513 dmd`D4ddmd4mars7tryMainFmPPxaZi + 14523 at mars.d:1448 frame #2: 0x00000001000033c3 dmd`_Dmain + 39 at mars.d:1618 frame #3: 0x0000000100264740 dmd`D2rt6dmain211_d_run_mainUiPPaPUAAaZiZ6runAllMFZ9__lambda1MFZv + 40 frame #4: 0x0000000100264668 dmd`D2rt6dmain211_d_run_mainUiPPaPUAAaZiZ7tryExecMFMDFZvZv + 32 frame #5: 0x00000001002646e5 dmd`D2rt6dmain211_d_run_mainUiPPaPUAAaZiZ6runAllMFZv + 45 frame #6: 0x0000000100264668 dmd`D2rt6dmain211_d_run_mainUiPPaPUAAaZiZ7tryExecMFMDFZvZv + 32 frame #7: 0x00000001002645db dmd`_d_run_main + 459 frame #8: 0x000000010000347e dmd`main + 34 frame #9: 0x00000001000016a4 dmd`start + 52

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