Segmentation fault on /jsonrpc

Potentially related to #621, except with /jsonrpc/history?=false, /jsonrpc/listgroups, and /jsonrpc. There is no output, unless the build is configured with --enable-debug.

When debug is enabled, here are the relevant lines in the log leading up to the crashes:

Sun Feb 21 05:30:02 2021        254     3061509484      DEBUG   Final URL=/jsonrpc/history?=false (WebServer.cpp:240:ParseUrl)                                                                            
Sun Feb 21 05:30:02 2021        254     3061509484      DEBUG   request received from 172.20.0.1 (WebServer.cpp:123:Execute)
Sun Feb 21 05:30:02 2021        254     3061509484      DEBUG   MethodName=history (XmlRpc.cpp:418:Dispatch)          
Sun Feb 21 05:30:02 2021        254     3061509484      ERROR   Segmentation fault

and:

Sun Feb 21 05:30:22 2021        283     3062213996      DEBUG   [/jsonrpc/listgroups] [...] HTTP/1.1 304 Not Modified [...] (WebServer.cpp:545:SendBodyResponse)
Sun Feb 21 05:30:22 2021        283     3062213996      DEBUG   Sending data (Connection.cpp:366:Send)
Sun Feb 21 05:30:22 2021        283     3061849452      ERROR   Segmentation fault

and:

Sun Feb 21 05:39:25 2021        299     3062607212      DEBUG   Final URL=/jsonrpc (WebServer.cpp:240:ParseUrl)
Sun Feb 21 05:39:25 2021        299     3062607212      DEBUG   Request=[...] (WebServer.cpp:120:Execute)
Sun Feb 21 05:39:25 2021        299     3062607212      DEBUG   request received from 172.20.0.3 (WebServer.cpp:123:Execute)
Sun Feb 21 05:39:25 2021        299     3062607212      DEBUG   MethodName=history (XmlRpc.cpp:418:Dispatch)
Sun Feb 21 05:39:25 2021        299     3062607212      ERROR   Segmentation fault

The [...] are my edits.

This is in a Docker container on Alpine 3.13, which appears to use musl 1.2.2, on a Raspberry Pi 4. I tested with 21.0, 21.1-r2311, and the tip of the dev branch. It worked fine on Alpine 3.12.